620 L. E. Cai!v. 



althoug'li ill liis form the germ cells are more closely crowded 

 together and are more regular in form, resembling a closely packed 

 mass of epithelial cells. 



When the conditions found in a young sporocj^st (Figs. 9 and 

 10) are compared with those present in older ones (Figs. 11 and 12) 

 it becomes at once apparent that there are two definite „broods" 

 of embryos (germ balls) formed inside the nurse generation. That 

 the first lot of eggs originated from cells which have come over in 

 the embryonic development without having been attached to the 

 body wall seems to me by far the more probable view. 



As shown in Fig. 10. there are no definite cells in the cyto- 

 plasmic layer of the body wall of the sporocyst at this stage. 

 Therefore to suppose that the eggs present in the body cavity at 

 that stage had arisen in the wall would necessitate the inference 

 that cells had been formed at some places in the wall and set free 

 from it before any regonizable activities in the way of cell differen- 

 tation had begun over the remainder of its area. 



Another difference is shown in comparing Figs. 9 and 12. In 

 the younger sporocyst many of the eggs in the body cavity are 

 undergoing the maturation division. In the older sporocyst one of 

 the eggs, still attached to the wall of the ovary, has already formed 

 the polar body. The study of other similar instances shows that in 

 the older sporocysts maturation commonlj' takes place before the 

 eggs are set free from the ovary. 



As has been pointed out by Korschelt & Heidee, in their 

 Text Book, there is really no fundamental difference in the egg 

 cells whichever may have been the mode of their origin. The whole 

 question is in reality one which concerns the location, and not at 

 all the nature, of the cells under discussion. 



Reuss (1903), Tennent (1905) and Rossbach (1906) figure divi- 

 ding germ cells still enclosed in the body wall, although Tennent 

 states that this is of rather uncommon occurence in Bucephalus. 

 He says, however, that the cells which he interprets as polar bodies, 

 are usually given off before the germ cells are set free from the 

 "Keimlager". In Diplodiscus I have never found a single instance 

 where the eggs had begun to segment before they were free in the 

 bod}' cavitj'-. 



Since the so-called „germ cells" in the nurse generations of the 

 Malacocotylea prove to be parthenogenetic eggs, the "Keimlager" 

 from which they arise must be an ovary, and on this ground a 



