Anatomical structure of Aspidogaster conchicola. 481 



throat. The ventral sucker may widen out past the sides of the body, 

 and then (Fig. 7) the lower half of the body walls — that portion 

 which belongs to the foot — slants outwards and downwards like the 

 buttresses of a building, and carries on its surface a series of ridges 

 inclined downwards, outwards and backwards. The posterior end of 

 the body possesses much less capacity to vary its form than the 

 anterior. From being bluntly rounded, however, it may project to a 

 considerable extent past the end of the ventral sucker; and then, this 

 projected part, by taking diiferent angles to the rest of the body, 

 sometimes resembles the neck. At its end is also to be seen an 

 indentation (Fig. 23) caused by the pulling forwards of the large 

 ventral excretory vessels. At the bottom of this pit are the two 

 excretory pores, which come to the surface as the projected end is 

 withdrawn. It may be expected that, in fixed animals, much variation 

 in form, as well as in displacements of internal organs, will occur. 

 They all live and move after coming into contact with the killing 

 fluid. Different reagents permit diöerent lengths of time to elapse 

 before the animal is killed and fixed all the way through. My most 

 normally shaped animals were obtained by pouring hot Gilson's fluid 

 onto them in a few drops of water in a watch glass. Under this 

 treatment they seemed to just have time enough to stretch out, when 

 they were fixed. Flemming's fluid kills slowly and of course from 

 the outside inwards, and the worms are generally much twisted. 



From these considerations, it seems to me that we cannot regard 

 the Aspidogaster limacoides of Diesing as a distinct species upon 

 the ground of the characters as given by Diesing and later by 

 VoELTZKOw. Among them is not a single character that can not be 

 accounted for as being occasioned through the method of killing and 

 the consequent conditions of contraction. All these variations have 

 come before me in Ä. conchicola. That Ä. limacoides was found in 

 the intestine of a fish may be some reason for suspecting a new 

 species ; but, at the same time, if the young of Ä. conchicola can live 

 in the intestine of the clam, they may also be able to live, for a 

 time, in the intestine of a fish, which has taken them up with its 

 food. I do not say that it is not another species, but that the cha- 

 racters, as given, are too indefinite. 



Cfeneral internal structure. 



The wide mouth-opening narrows backwards in a funnel form, to 

 the closed muscular pharynx, which is succeeded by an intestine in 



