200 ILLINOIS BIOLOGICAL MONOGRAPHS (488 



dropping ofif of two or more very immature segments from the hinder end. The 

 first indication of this is probably represented in figure 52, altho the strobila 

 in figure 53 does not show it. The relative ages, however, of these two is 

 difficult to state definitely since the first one is more contracted longitudinally 

 than the other. On the other hand, two intermediate in length between those 

 shown in figures 53 and 54, were indented posteriorly, thus showing that some 

 of the earliest segments had already been lost. Thus it is seen that at a very 

 early period in the development of the strobila of this species there are lost 

 a few of the first-formed segments in much the same way as the bladder of the 

 cysticercus of the taenioid cestodes is cast off in the final host. 



The material studied consisted of lots 86, 87, 88, 303 and 304 from Salmo 

 salar, 38a, b, c, d, e, and o, 66, 67, 164, 167 and 192 from Cristivomer namaycush, 

 42 and 166 from Coregonus dupeiformis, and 61, 62, 381, and 387 from Zo/<z 

 maculosa, in the writer's collection; Ch 26a, Ch 26b, Ch 29a, Ch 29b, Ch34a, 

 Tig, T2q and 17.186 from C namaycush, and Ch 13b and Ch 22b from Lota 

 maculosa, in the collection of the University of Illinois; and 509c, 511a, 520b, 

 524a, 525a and 530a from Salvelinus fontinalis , 613b and 622d from Lota macu- 

 losa and 616-620c from " whitefish, " in the collection of Dr. G. R. LaRue. 



