494 ALBERT W. BROWN. 



form the excretory bladder. These large trunks run the 

 whole length of the animal. About halfway each gives oflF a 

 branch vessel, which runs near the lateral surface of the body 

 backward nearly to the excretory pore. 



The two main branches run on to the anterior end of the 

 animal, when they become transverse, and, meeting in the mid- 

 line, form a vessel running backwards as far as the ventral 

 sucker. 



All these vessels give off at intervals, and finally break up 

 into smaller and smaller branches, each of which ultimately 

 ends in a dilated vesicle containing a rounded body called 

 by Fraipont " calcareoiis body.'^ The calcareous bodies 

 appear to be in a semi-fluid condition, and contain a good 

 deal of calcium carbonate. On treatment with acid they 

 dissolve and disappear^, and at the same time give off 

 gas. They are non-crystalline, and occupy nearly the 

 entire terminal vesicle. In the centre of these calcareous 

 bodies may be seen one or two bright dots looking like 

 granules. In some cases I have found the terminal vesicles 

 quite empty. 



In Diplostomum volvens Fraipont described a more 

 dorsal network composed of very fine tubules ending in flame- 

 cells. This finer network joined the main trunk of the 

 coarser at about one third of the entire length from the 

 anterior end of the animal. Now I have seen flame-cells 

 throughout the entire body of Tetracotyle petromyzontis 

 in the dorsal region, but I am quite unable to assert the 

 existence of a definite network joining the coarser part at a 

 given point. My endeavours to see such a network have 

 ended fruitlessly, although I have made many attempts, for 

 the tubes are excessively minute and seem capable of occlu- 

 sion at times. Consequently my observations only enable me 

 to assert the existence of flame-cells forming scattered portions 

 of network, but whether these communicate with tiie rest of 

 the system, as in Diplostomum volvens, or at many points 

 near the terminal vesicles — as 1 have imagined them to do in 

 several cases — I am unable to say definitely. 



