618 L- R- Cary, 



bei allen 3 Formen ihre Entstehung- aus einem Keimlager, welches 

 aus embrj^onalen, bei der Organentwicklung- des Tieres nicht ver- 

 brauchten Furchungselementen besteht (5). Dieses Keimlager bildet 

 bei den Embryonen eine epitheliale Auskleidung der Leibeshöhle, 

 es lokalisiert sich bei den Redien bis zur Bildung eines förmlichen, 

 aber noch wandständigen Keimstockes, welcher bei den Cercarien 

 als noch mehr individualisiert und in das Innere des Leibes gerückt 

 aufgefaßt werden darf." 



In Diphdiscus temporains the facts seem to me to support the 

 opinion set forth by Thomas, namely: that the germ cells in the 

 sporocyst may be traced directly to the o^^g, or that they may 

 arise in the body wall of the sporocyst. 



A comparison of Figs. 9, 10, 11, 12 and 13. which represent 

 sections through sporocysts of diiferent ages, will show the grounds 

 for this conclusion. In Fig. 9, which is a section through one of 

 the youngest sporocysts found, the only cells pi-esent in the body 

 cavity are several eggs more than half of which are undergoing 

 the maturation division. In the wall of the sporocyst there are 

 many nuclei in a homogeneous layer of cytoplasm. 



In a section through an older sporocyst, as is represented in 

 Fig. 10, the body cavity contains a considerable number of eggs, 

 practically all of which are in the same stage of development. Of 

 the whole number found in this section, only one has undergone 

 the first segmentation division, while seven show a polar body 

 attached. At this stage in the development of the sporocyst the 

 internal layer of the body wall is made up of a layer of cytoplasm 

 in which there are present a number of nuclei. This cytoplasmic 

 layer is of practically the same thickness throughout its extent. 

 The nuclei are uniformly distributed around the whole circumference 

 of the body wall, and are of practically the same size. 



In a still older sporocyst (Fig. 11). — the greater age is shown 

 by the development of the contained embrj^os — there is shown the 

 beginning of the localisation of the cytoplasm and nuclei to form 

 the ovary (Keimlager). On one side of the sporocyst the cytoplasmic 

 layer of the body wall still retains a character similar to that shown 

 in Fig, 10. On the opposite side, however, the thickness of the 

 layer has increased to more than twice that of the former side. 

 In the deepest part of the ovary each nucleus is surrounded by a 

 definite mass of cytoplasm which has a sharp outline: a cell wall. 

 All of these cells which were cut in the proper plane show an 



