SEA-FISHERIES LABORATORY. 139 



looser and finally disappears. The intestine is then a 

 simple, thin-walled tube. 



There is a very distinct intestinal musculature 

 From the posterior wall of the pharynx a series of strong 

 muscle bundles take origin and pass backwards slightly 

 obliquely to be inserted into the walls of the oesophagus 

 just behind the pharynx. From here to the extremity 

 of the intestinal branches these longitudinal muscles 

 persist. They always appear in transverse sections of the 

 body as little protuberances on the external surface of the 

 intestine. They do not, however, form very long bundles, 

 but are attached at intervals to the surface of the gut 

 forming a series of short loops. They run quite longitu- 

 dinally, and not at all obliquely. It is these longitudinal 

 muscles which produce the peristaltic movements of the 

 intestine. Circulai muscle fibres are not to be seen in 

 section, and are probably absent. But here and there the 

 gut is attached to the lateral walls of the body by fibrous 

 bundles, many of which appear to be muscular, and the 

 contractions of these extrinsic intestinal muscles are pro- 

 bably antagonistic to" those of the intrinsic longitudinal 

 system. 



The ventral sucker is situated rather nearer to the 

 anterior, than to the posterior extremity. It is not quite 

 round in shape ; the longitudinal diameter is the larger 

 in my specimens. The shape of the opening is, of course, 

 variable, but is usually triangular. This sucker possesses 

 a strong extrinsic musculature. All round its ventral 

 periphery strong bundles of muscular and connective 

 tissue take origin and run out radially to be inserted 

 into the lateral and ventral body walls. Some run dorso- 

 ventrally and are inserted into the dorsal body walls. 

 These muscles, originating m the periphery of the ventral 

 sucker, appear to constitute the principal system of 



