physical violence. An evolutionary divergence between stomatopods is described in appearance of the meral spot, which is a dorsal, medial groove on the raptorial merus of the raptorial appendage. Smasher stomatopods, which are species that tend to inhabit cavities within rocks or coral, have brightly coloured meral spots which aid in making the meral spot more visible during these meral spread displays in fights. These bright meral spots possessed by smashers are either yellow, blue, red or white and are outlined by a conspicuous black pigment. Conversely, spearing Stomatopods or some smashing species that do not inhabit rock or coral cavities, have much duller meral spots. This correlation suggests to researchers that habitat and meral spot colouration have co-evolved, and those that inhabit burrows possess these bright spots and those species that do not have dull spots. This demonstrates how ecology and evolution of organisms within the same order directly affects agonistic behaviour. Hormonal influence Agonistic behaviour is influenced by the action of hormones such as vasopressin, which is a small peptide synthesized in the brain by magnocellular neurons. Agonistic behaviour itself may be divided into two categories: offensive or defensive. Each of these classes of agonistic behaviour are the result of different neurobehavioural pathways, and offensive and defensive agonistic behaviour are elicited by different stimuli. Offensive behaviour specifically has been studied in the context of intruder interactions in studies employing rodents as test subjects. For example, when an unfamiliar male hamster is placed into cage of a conspecific male, a stereotypical suite of agonistic behaviours follow. The resident male approaches the intruder and sniffs him intently, threatens the intruder with an upright posture, and finally initiates a physical attack on the intruder. The resident male attacks the belly of the intruder male and attempts to maneuver the intruder onto his back. Studies have shown that offensive behaviour displayed by hamsters may be modulated due to the presence of vasopressin. Specifically, research conducted by Ferris et al. (1990) suggests that when a vasopressin receptor antagonist is injected into the anterior hypothalamus of the resident male, the tendency to attack intruder males decreases as the dose of antagonist increases. This antagonist has been known to decrease the tendency of offensive aggression via injections into the ventrolateral hypothalamus, therefore is able to act on multiple regions of the brain and exhibit the same effects of offsetting this agonistic behaviour. While vasopressin plays