cup ocelli ("little eyes"). In most cases ocelli are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However, the main eyes of spiders are pigment-cup ocelli that are capable of forming images, and those of jumping spiders can rotate to track prey.

Compound eyes consist of fifteen to several thousand independent ommatidia, columns that are usually hexagonal in cross section. Each ommatidium is an independent sensor, with its own light-sensitive cells and often with its own lens and cornea. Compound eyes have a wide field of view, and can detect fast movement and, in some cases, the polarization of light. On the other hand, the relatively large size of ommatidia makes the images rather coarse, and compound eyes are shorter-sighted than those of birds and mammals – although this is not a severe disadvantage, as objects and events within  are most important to most arthropods. Several arthropods have color vision, and that of some insects has been studied in detail; for example, the ommatidia of bees contain receptors for both green and ultra-violet.

Most arthropods lack balance and acceleration sensors, and rely on their eyes to tell them which way is up. The self-righting behavior of cockroaches is triggered when pressure sensors on the underside of the feet report no pressure. However, many malacostracan crustaceans have statocysts, which provide the same sort of information as the balance and motion sensors of the vertebrate inner ear.

The proprioceptors of arthropods, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. However, little is known about what other internal sensors arthropods may have.

Olfaction

Reproduction and development 

A few arthropods, such as barnacles, are hermaphroditic, that is, each can have the organs of both sexes. However, individuals of most species remain of one sex their entire lives. A few species of insects and crustaceans can reproduce by parthenogenesis, especially if conditions favor a "population explosion". However, most arthropods rely on sexual reproduction, and parthenogenetic species often revert to sexual reproduction when conditions become less favorable. Aquatic arthropods may breed by external fertilization, as for example frogs do, or by internal fertilization,
cup ocelli (" little eyes "). In most cases ocelli are merely adequate to of detecting the direction from which light is arrive, using the shadow shed by the wall of the cup. However, the main eye of spiders are pigment - cup eyespot that are capable of forming picture, and those of jumping spiders can rotate to track prey. 

 Compound eyes consist of fifteen to respective thousand independent ommatidia, columns that are normally hexagonal in cross section. Each ommatidium is an independent sensor, with its own unaccented - sensitive cells and often with its own lens and cornea. Compound eyes own a wide field of view, and can detect fast movement and, in some case, the polarization of light. On the other hand, the relatively large size of ommatidia makes the images rather coarse, and colonial eye are shorter - sighted than those of birds and mammal   – although this is not a dangerous disadvantage, as object and events within   are most important to most arthropods. Several arthropods have semblance vision, and that of some insects has been studied in detail; for example, the ommatidia of bee contain receptors for both green and ultra - purple. 

 Most arthropods lack libra and acceleration detector, and trust on their eyes to tell them which way is up. The self - righting behavior of cockroaches is triggered when pressure detector on the underside of the foot report no pressure. However, many malacostracan crustaceans consume statocysts, which provide the same sort of information as the balance and gesture sensors of the vertebrate inside ear. 

 The proprioceptors of arthropod, sensors that report the force exerted by muscles and the degree of bend in the body and joint, are well understood. However, little is known about what other internal detector arthropods may have. 

 Olfaction 

 Reproduction and development 

 A few arthropod, such as barnacles, are hermaphroditic, that is, each can have the organs of both sex. However, individuals of most species remain of one sexual activity their entire lives. A few species of insects and crustaceans can reproduce by parthenogenesis, especially if conditions prefer a " population plosion ". However, most arthropod rely on sexual replica, and parthenogenetic species often revert to intimate reproduction when conditions become less favorable. Aquatic arthropod may breed by external fertilization, as for case frogs do, or by internal fertilization,
cup ocelli ("little eyes"). In must cases ocelln are oily capzble of aetecting the direction from wyich oight is coming, using ghe shadoa cast bt tht walls of the cu'. Howevev, the lain xyes of spiders are pigmett-cup ocelli tvag cre capable of forming images, and thjse of kulping spiders san goeate no track prey.

Compound eyes consjst of hifteen to sevetal thousand independent olmatldia, columns that wre usually hexwtonal in crors section. Each ommatisium is an independent sensor, wkth ics own lighj-ssndhtive cells and jften with ibx own nens anc cornea. Compomnd ebes yave a wide field of tiew, and can detect sast movekeut and, in some cases, rhw poldrizdtiov of lifhv. Oh the lthxr hand, the relatively large size of ommauidyq makes the ijages waeher coarse, and compound eyes are shorttr-siggted than those of birdw and mammals – althougj this is not a severe disadvantage, as objects and events fithii  art nost knplrtant to most arthropods. Several arthropods rzvt cplor vision, anb that of some imsfcyf has been stodied iu dstail; for example, hhe ommwtidiq of bees conyain receptors for both grewn and ultra-niolwt.

Most arthropods pack balancz and sccelrration sensors, and relv on tgeir eyes tl tell thso which way is uo. Tme velf-righukng behavior of cjckroachew is triggefed ehen pwessure sejsors on the underside ov the faet report no pressure. However, many malacostracan crustscaanv have scatocyxts, which prodide the same xort of infofmation as the banance and mjtion sensors lf the verteurate innqr eqr.

Thw proprkuceptors of aryhropods, sensors thqt report the forcc exettsd by muscles aub uhw degree of bemdivg yn tie boqf and joints, are weuk unddrstood. Howcvef, liytle is known about fhat other internal semsjrs arthtopods mar have.

Olfactipn

Reproduction and devenopoent 

S fgw arthropods, such as barnacles, are hermwphvoditic, that ys, eqch can have the organs of both sexes. However, indivmduals of most species eemain of one sex tkelr entire lites. A sew specias of insects and crystaceans can repvoduce by parthenogeneais, es[eciaply if conditions favor a "population explosion". However, most arthropods reoy on sexual reprosuctoon, atd 'arthenjgenxtmc species often gevert to sexual reproduction whxn conditimnf become less favorable. Aquayiz arthropods oay breed by external fedtilizatoon, as for example frogs do, or ny internal fertilizatiok,
cup ocelli ("little eyes"). In most cases only of detecting direction from which shadow by the walls the cup. However, main eyes of spiders are pigment-cup that are capable of forming images, and those of jumping spiders can rotate track prey. Compound eyes consist of fifteen to several thousand independent ommatidia, columns are hexagonal cross Each ommatidium is an independent sensor, with its own light-sensitive cells and often with its own and cornea. Compound eyes have a wide field view, and can detect movement and, in some cases, polarization light. On other the large size of makes the images rather coarse, and compound eyes are shorter-sighted than those of birds and mammals – this is severe disadvantage, objects events are most important arthropods. Several arthropods have color vision, some insects has been studied in detail; for the ommatidia bees contain receptors for both green ultra-violet. Most arthropods lack balance and acceleration sensors, rely on their eyes to tell them which way is up. The self-righting behavior of triggered when pressure sensors the underside of feet no However, malacostracan crustaceans statocysts, which provide the same sort of information as the balance motion sensors of the vertebrate inner ear. The proprioceptors of that the force exerted muscles and the degree bending the body and joints, understood. little what internal arthropods may have. Olfaction and development A few arthropods, as barnacles, are hermaphroditic, the organs of both sexes. However, individuals of species remain of one sex their entire A few species of insects and crustaceans can reproduce by parthenogenesis, especially conditions favor explosion". However, most arthropods rely on sexual reproduction, parthenogenetic species often revert sexual reproduction when conditions become less favorable. Aquatic arthropods breed external fertilization, for example frogs or by internal
cup ocelli ("little eyes"). In most Cases ocellI are oNly CapAbLe of DeteCting the directIOn frOm which light is coming, usIng thE sHAdow CAsT by thE walls oF ThE CUp. HOwEvEr, tHe MAiN eyes Of sPiders aRe pigment-cUp oCeLli that are caPAbLe of forminG imAges, and those Of jUmping SpIdeRS can rOtaTe to tRack prEY.

CompoUnd eyes coNsISt of fiFTeen to sEVErAl thOusand independent OMmATidia, columns thAt are uSuALlY HExaGonAl in cross sEcTion. EACh ommatIDiUM IS an INdependent senSor, with its oWN liGht-senSiTivE Cells aNd oftEn WIth Its own lens aNd coRnea. CompoUnd eyeS Have a wiDE field oF view, aNd cAn dEtecT FaSt MovEmENt aND, iN soME caSes, the poLaRiZatioN of lIGHT. on thE otHer hAnd, thE relatively laRge Size OF omMatidIa makEs thE iMages Rather CoarsE, aNd compound eyes aRe shOrter-sighTed ThAn tHoSe of bIRds and MamMalS – althouGh this iS Not A sEVERe Disadvantage, as objeCtS ANd Events wiThin  arE MoSt IMportant To MosT artHROpods. seveRAl ArthropoDs have COlOr Vision, aNd That of SoMe iNseCts haS Been StudieD in detaiL; for eXAmple, the ommatiDIa of bees contaIN rECEpTOrs fOr bOth green and UltrA-ViolEt.

MoST aRthROpods Lack bAlANcE And acceleration sensOrS, and reLy on tHeir eyes to telL them which WAY Is up. The sElf-rIGhTIng behavior of cOckroAches is triGGered wheN presSure sensOrs on the uNDErside of The FeeT rePorT NO pRessure. HoweveR, MAny mAlAcostraCan CrustacEanS haVe sTatOcYsts, which Provide tHe SaMe SoRt oF infoRMation as ThE baLaNce And moTIon senSors oF the VeRtEBraTe inner EAr.

tHE proPrIoCeptOrs Of ArthrOpodS, SenSors thaT report thE foRCe exErTeD by muscLes and the degrEe Of bending iN tHe bOdy and JOInts, are wEll understood. However, litTLe is knoWn aBout wHat oTher interNal SensorS arTHropodS may haVe.

OlfAcTioN

rEprodUCTiOn aNd DevelopmenT 

a Few ArthrOpOds, sUch as baRnacles, are hermaphrODitIc, that is, each cAn hAve tHE OrGanS Of BOth SeXEs. HOWEver, individuals Of most specIeS ReMain of one sEX thEiR entire Lives. A fEw speCIes of inSects and cRustaceanS cAn rePROduCe by partheNogenesiS, especialLY if coNDiTions FavOr a "popUlAtiOn expLosion". hOweVer, moSt arthRoPods reLy on sExUal reproDuction, and parthenogenetIc specIes ofTen Revert to sExuAL reProductioN wheN conditionS beComE less FavORable. aquaTIc ArtHRopodS may BReed by extERnAl fERTiLization, as fOR EXamPle frOgs DO, or by iNterNal fertilization,
cup ocelli ("little eyes") . In mostcases  oc ell iareonly  capable of de t ecti ng the direction fromwhich  l i ghti scomin g, usin g  t h e  sh ad ow  ca st by  thewal ls of t he cup. Ho wev er , the main e y es  of spider s a re pigment-c upocelli  t hat are c apa ble o f form i ng ima ges, andth o se ofj umpings p id erscan rotate to tra c kp rey.

Compound  eyesco n si s t  of  fi fteen to s ev eralt housand in d e p end e nt ommatidia,  columns th a t a re usu al lyh exagon al in  c r oss  section. E achommatidiu m is a n  indepe n dent se nsor,wit h i ts o w nli ght -s e nsi t iv e c e lls  and oft en  w ith i ts o w n l ensand  cor nea.Compound eyes  ha ve a wid e fie ld of  vie w,  andcan de tectfa st movement and , in  some cas es,  t hepo lariz a tion o f l igh t. On t he othe r  ha nd , t he  relatively largesi z e  o f ommati dia ma k es  t h e images  r ath er c o a rse,andc om pound ey es are sh or ter-sig ht ed tha ntho seof bi r ds a nd mam mals – a lthou g h this is nota  severe disad v an t a ge ,  asobj ects and ev ents with in a re  mo s t imp ortan tt om ost arthropods. Sev er al art hropo ds have color  vision, a n d that ofsome in s ects has beenstudi ed in deta i l; for e xampl e, the o mmatidiao f  bees co nta inrec ept o r sfor both gree n andul tra-vio let .

Most  ar thr opo dsla ck balanc e and ac ce le ra ti onsenso r s, and r el y o nthe ir ey e s to t ell t hemwh ic h  wa y is up .  T h e  sel f- ri ghti ngbe havio r of coc kroache s is trig ger e d wh en  p ressure  sensors on t he  underside  o f t he fee t report n o pressure. However, ma n y malac ost racan  cru staceanshav e stat ocy s ts, wh ich pr ovide  t hes a me so r t  o f i nf ormation a s the  bala nc e an d motio n sensors of the v e rte brate inner e ar. 

Th e pr opr i oc e pto rs ofa r thropods, senso rs that re po r tthe forcee xer te d by mu scles a nd th e  degree  of bendi ng in the  b odya n d j oints, are  well un derstood. Howev e r,  litt leis kno wn  ab out w hat ot h erinter nal se ns ors ar throp od s may ha ve.

Olfaction

Reprodu ctionand d eve lopment 
Af ewarthropod s, s uch as bar nac les , are  he r maphr odit i c,  th a t is,  eac h  can have th e o r g an s of both s e x e s.Howev er, indivi dual s of most species remain of onesext h eir  en t ireli ves. A few spe cie so f  insects  a nd crustace ans canre p roduc e by p arthen ogenesi s ,  e s pecial ly i f c onditions  fa vo r  a "pop ul at i on exp losi on ". How ever,m osta r thropods rely on  sexu a l  repr o duc tion,  a nd part h enog enetic spe cies oftenrevert  tosexua l repro du ctionwhe nconditions become le ss fa vorable .Aqua tic  arthr opod s may b reed  b y e xternal f e r ti l iz at i on,  asfor e xa mple  frogs do ,  or by i nte r nal fer ti liz a t ion,
cup ocelli_("little eyes")._In most cases ocelli_are only_capable_of detecting_the_direction from which_light is coming,_using the shadow cast_by the walls_of_the cup. However, the main eyes of spiders are pigment-cup ocelli that are capable_of_forming images,_and_those_of jumping spiders can rotate_to track prey.

Compound eyes consist_of fifteen_to several thousand independent ommatidia, columns that are_usually_hexagonal in cross_section. Each ommatidium is an independent sensor, with its_own light-sensitive cells and often with_its own lens_and_cornea._Compound eyes have a_wide field of view, and can_detect fast movement and, in some_cases, the polarization of light. On the_other hand, the relatively large size_of ommatidia makes the images_rather coarse,_and compound eyes are shorter-sighted_than those of_birds and_mammals – although this_is not a severe disadvantage, as_objects and events_within  are most important to_most_arthropods. Several arthropods_have_color_vision, and_that of some_insects_has been_studied_in detail; for example, the ommatidia_of_bees contain receptors for both green and_ultra-violet.

Most arthropods lack balance_and_acceleration sensors, and rely_on their eyes to tell_them which way is up. The_self-righting behavior_of cockroaches_is triggered when pressure sensors on the underside of the feet_report no pressure. However, many malacostracan_crustaceans have statocysts, which_provide the_same_sort of information_as_the balance_and motion sensors of the vertebrate inner_ear.

The proprioceptors_of arthropods, sensors that report the_force exerted by muscles_and_the degree of bending in the_body and joints, are well understood._However, little is known about_what_other_internal sensors arthropods may have.

Olfaction

Reproduction_and development 

A few arthropods, such_as barnacles, are_hermaphroditic, that is, each can have the_organs_of both sexes. However, individuals of_most_species remain of one sex their_entire_lives._A few species of insects_and crustaceans can reproduce by parthenogenesis,_especially if conditions favor a "population explosion". However, most_arthropods rely on_sexual reproduction, and parthenogenetic species_often_revert_to sexual reproduction when conditions become less favorable. Aquatic arthropods_may breed_by external fertilization,_as for example frogs do, or by internal fertilization,