STRUCTURE OF CLINOSTOMUM 207 



identical with blood corpuscles taken from the heron. This 

 substance is evidently food, but the content of the caeca of the 

 bass worm cannot be so considered. Its prompt rejection from 

 the body as soon as it is liberated from the cyst would be evidence 

 sufficient to justify this conclusion. Its crystalline form and the 

 fact that it is discharged as soon as the animal becomes free, point 

 to the hypothesis that the cavities of the intestine are made use 

 of for storage during encystment and that the substance therein 

 is a waste product. 



THE EXCRETORY SYSTEM 



The excretory system of C. marginatum has never been de- 

 scribed. The indications of it which are given in Looss ('85, fig. 

 22) are purely diagranmiatic and somewhat misleading. The 

 system, moreover, presents some features which are very unusual, 

 so that the whole subject needs a careful revision. 



The location of the excretory pore has already been noted. It 

 opens from a very short duct (fig. 15) which is in communication 

 with the v-shaped bladder. Internally the two branches of the 

 bladder receive the termination of the collecting tube in the center 

 of a flattened area. At the excretory pore there is an invagina- 

 tion of the cuticle which covers the outer surface of the body. 

 As this passes more deeply it gradually changes into a cubical 

 epithelium composed of nucleated cells identical in structure with 

 those which make the wall of the collecting vessel. At inter- 

 mediate points epithelial cells of the bladder show all stages of 

 degeneration in structure and pass insensibly into cuticle. There 

 is no muscular tissue in the walls of the bladder. Living speci- 

 mens were observed particularly with reference to contractions 

 in the bladder as I had found this organ in Cotylaspis interesting 

 in this respect ('94, p. 216) but the walls were not contractile. In 

 correlation with this is the absence of a sphincter at the surface 

 pore (one is present in this place in Cotylaspis) and the presence 

 of a sphincter at the junction of the collecting vessel and the blad- 

 der. We may conclude from the position of the sphincter and the 

 non-contractiUty of the bladder that the latter in Clinostomum is 



