ON TETRACOT^LE PETROMYZONTIS. 493 



layers of muscles. The longitudinal bands of muscle are 

 quite easily visible in the animal without the aid of sections. 

 They extend almost the entire length of the body, except in 

 the region of mouth and lateral adhesive organs, where the 

 musculature has a circular arrangement. The general mass 

 of the body is filled with a highly vacuolated parenchynaatous 

 tissue, the ultimate structure of which is very difficult to make 

 out. In this lie the main organs of the body. 



The intestine does not call for special mention. The fork 

 of the intestine is occupied by a mass of gland-cells which 

 extend on each side, forming a zone across the animal. These 

 cells stain very readily, and show up in strong contrast with 

 the general parenchyma of the body. They are filled with 

 material of a slightly more yellow tinge. The space between 

 the intestinal fork and the ventral sucker is entirely filled 

 with them. 



These gland-cells communicate with the retractile ear- 

 shaped structures on the sides of the oral region, and open 

 there to the exterior by fine canals. The " ears " themselves 

 are retracted by a series of longitudinal muscles shown in 

 fig. 6, which appear to be specially differentiated longitudinal 

 muscles. 



I was able to trace out the fine tubes leading from the 

 gland-cells in several sections. Their connection with the 

 cells in the intestinal fork is not so easily seen, but I am 

 convinced that they do communicate with part of them at 

 least, both groups of cells being similar in histological 

 characters. Both group of cells, then, are connected either 

 wholly or in part with the antero-lateral retractile pro- 

 cesses. 



Excretory System. — This system of organs commands the 

 most interest. Fraipont, in ' Archives de Biologic, I,' has 

 given an account of the excretory system of Diplostomum 

 volvens which agrees pretty closely with this. It consists of 

 two parts — a coarser, and a finer and more dorsal portion. 



The coarser part leads from the excretory pore in the form 

 of two main trunks, whose terminal portions are dilated to 



