, ▁tub ular ▁and ▁solid ▁structures , ▁and ▁discrete ▁groups ▁of ▁tum or ▁cells ▁( Fig . ▁ 2 ). ▁The ▁al ve olar ▁structures ▁are ▁tum or ▁cell ▁clusters ▁of ▁round ▁or ▁slightly ▁irregular ▁shape . ▁The ▁morph ology ▁of ▁the ▁cells ▁that ▁form ▁this ▁type ▁of ▁structures ▁var ies ▁from ▁small ▁cells ▁with ▁moder ate ▁cy top las m ▁and ▁round ▁nuc lei ▁to ▁large ▁cells ▁with ▁hyper chrom atic ▁nuc lei ▁of ▁irregular ▁shape ▁and ▁moder ate ▁cy top las m . ▁The ▁trab ec ular ▁structures ▁are ▁either ▁short , ▁linear ▁associations ▁formed ▁by ▁a ▁single ▁row ▁of ▁small , ▁rather ▁mon omorphic ▁cells ▁or ▁wide ▁cell ▁clusters ▁consisting ▁of ▁two ▁rows ▁of ▁medium - s ized ▁cells ▁with ▁moder ate ▁cy top las m ▁and ▁round ▁norm och rom ic ▁or ▁hyper chrom atic ▁nuc lei . ▁The ▁tub ular ▁structures ▁are ▁formed ▁by ▁a ▁single ▁or ▁two ▁rows ▁of ▁rather ▁mon omorphic ▁cells ▁with ▁round ▁norm och rom ic ▁nuc lei . ▁The ▁solid ▁structures ▁are ▁fields ▁of ▁various ▁sizes ▁and ▁shapes , ▁consisting ▁of ▁either ▁small ▁cells ▁with ▁moder ate ▁cy top las m ▁and ▁mon omorphic ▁nuc lei ▁or ▁large ▁cells ▁with ▁abund ant ▁cy top las m ▁and ▁polym orph ic ▁nuc lei . ▁Dis crete ▁groups ▁of ▁cells ▁occur ▁in ▁the ▁form ▁of ▁clusters ▁of ▁one ▁to ▁four ▁cells ▁with ▁variable ▁morph ologies . <0x09> ▁ <0x09> ▁ <0x09> ▁ <0x09> ▁According ▁to ▁the ▁data ▁accum ulated ▁to ▁date , ▁it ▁may ▁be