PHYSIOLOGY OF THE INVERTEBRATA. 53 



tion of the transverse muscles of the labrum mentioned above 

 are found adjoining its anterior wall. The intestine (Fig. 1 1), 

 as in the other forms of the Pliyllopoda, constitutes a rather 

 wide and uniform tube, running along the axis of the body, 

 but very slightly dilated in its anterior part, that curves more 

 or less abruptly downward, according to the attitude of the 

 head. The foremost part of the intestine, extended within 

 the preoral part of the head, expands at the end on either 

 side to a very short and broadly rounded cascum, quite simple, 

 without any trace of folds or lobes, and communicating with 

 the intestinal cavity by a wide opening." 



In Cydcstheria liislopi there is no pancreas or so-called liver 

 filling up a great part of the anterior end of the body. The 

 total want of this organ is a striking feature, as it is present 

 in all other known bivalve Phyllopoda. In this respect 

 Cydestheria occupies a lower rank than the Pranchipodidce, in 

 which the digestive tubules are found to be at least more 

 or lees distinctly folded or lobed. " The structure of the in- 

 testinal tube (of Cydestheria) is that usually met with, its 

 walls being rather thin and surrounded by numerous circular 

 muscles. At the end of the trunk the intestine terminates 

 with a well-defined rectum, traversing the caudal part close 

 to its ventral side, and opening at its extremity between the 

 two caudal claws. The latter part of the intestinal canal is 

 very strongly muscular and generally devoid of contents, 

 except when at intervals the excrements are expelled from 

 the anal orifice." 



According to Dr. Sars, the food of Cydestheria consists of 

 vegetable matter (e.g., Algm, Desmidice, Diatomeoe, and Con- 

 fervce). The contents of the alimentary canal are of a yellow 

 colour in its anterior part, becoming gradually darker poste-" 

 riorly, and the excreta are invariably of a dark-brown colour. 

 " Hh.efood is conveyed to the mouth by the rhythmical move- 

 ments of the legs, which give rise to a whirling motion, 

 whereby any small particles suspended in the surrounding 

 water are sucked between the valves and brought into the 



