62 C. F. ROUSSELET ON THE ROTIFERA OF DEVILS LAKE 



sity, who has lately published an account of similar changes 

 in A. amphora found by him in a brackish pool, it is caused by a 

 change of diet, from vegetable to more substantial animal food, 

 and even cannibalistic fare. Prof. Powers found that the 

 animals hatched from resting-eggs were invariably saccate, and 

 that the humped and larger campanulate forms developed from 

 these. 



Asplanchna Silvestrii is a very large and powerful animal, as 

 is shown by its ability to capture, swallow and digest the 

 large and vigorous Diaptomus which abound in this lake ; one 

 of these Copepods was seen to more than fill its stomach. 



The male was also found ; it is humped, but the side humps 

 are not bind as in the humped female, as shown in figs. 5 

 and 6 ; the fertilised resting-egg is represented in fig. 9. The 

 jaws are of the usual type, but are different from those of any 

 other species of the genus, as is shown by fig. 7. The rami 

 are massive, and have a semi-circular cut-out near the tip, 

 which is peculiar ; they have also a strong basal hook and 

 median inner tooth. One of the rami, the one on the right 

 side when the basal hooks are uppermost, has a broad flange 

 near its apical tooth ; this serves as a stop for the opposite 

 tooth to prevent the two rami overlapping and interlocking. 



The prominent lateral humps differ markedly from those of 

 other humped species, such as A. Sieboldii and A. amphora. In 

 A. Silvestrii these are bifid, having a constriction, more or less 

 pronounced, above the middle of the hump, giving it a double 

 rounded outline (fig. 1) ; on the dorsal side there is a pointed 

 hump near the middle of the body (fig. 2). In intermediate 

 forms the humps are less prominent until the purely saccate 

 form is reached (fig. 3), which in shape does not much 

 differ from that of A. Brightwelli. Prof. Powers has shown 

 that no single animal goes through these various shapes ; they 

 are born with the shape they possess and do not change it in 

 their lifetime, but their jDrogeny may have a different shape 

 from the parent. A young humped individual may be seen in 



