958 



CRUSTACEA 



a proboscis-like projection, at the extremity of which is the narrow 

 orifice of the mouth, which draws in the semi-fluid aliment. Instead 

 of being furnished (as in the higher crustaceans) with two pairs of 

 antennae and numerous pairs of * foot-jaws,' it has but a single pair 

 of either ; it also bears four minute ocelli, or rudimentary eyes, set 

 at a little distance from each other on a sort of tubercle. From 

 the thorax proceed four pairs of legs, each composed of several joints, 

 and terminated by a hooked claw ; and by these members the 

 animal drags itself slowly along, instead of walking actively upon 

 them like a crab. The mouth leads to a very narrow oesophagus 

 (a), which passes back to the central stomach (b) situated in the 



FIG. 719. Ammothea pycnogonoides : a, narrow oesophagus ; 

 &, stomach; c, intestine ; d, digestive caeca of the foot-jaws ; 

 e, e, digestive caeca of the legs. 



midst of the thorax, from the hinder end of which a narrow intes- 

 tine (c) passes off. to terminate at the posterior extremity of the 

 body. From the central stomach five pairs of crecal prolongations 

 radiate, one pair (d) entering the foot-jaws, the other four (e, e) 

 penetrating the legs, and passing along them as far as the last joint 

 but one ; and those extensions are covered with a layer of brownish - 

 yellow granules, which are probably to be regarded as a digestive 

 gland. The stomach and its caecal prolongations are continually 

 executing peristaltic movements of a very curious kind ; for they 

 contract and dilate with an irregular alternation, so that a flux and 

 reflux of their contents is constantly taking place between the 

 central portion and its radiating extensions. The peri visceral space 

 between the widely extended stomach and the walls of the body and 



