2O2 GEORGE W. TANNREUTHER. 



of the embryonic foot and the mouth. A distinct epithelium or 

 hypodermis is present. The stomodaeum in the male embryo 

 is less prominent (B-C, 10), than in the female. The buccal 

 pouch and pharynx is derived from this invagination. The 

 posterior wall of the pharynx (A-C, n) is more prominent in the 

 female and contributes directly to the formation of the jaws or 

 trophi. There is no indication of the formation of trophi in the 

 male embryos. 



E. THE ROLE OF THE ENTODERMAL AND THE REPRODUCTIVE 



CELLS. 



The early differentiation of the derivatives of E bears a striking 

 resemblance in the two sexes (A-C, 11). Two distinct regions 

 are readily recognized. The upper and anterior part (st.) be- 

 comes continuous with the walls of the pharynx, and in the 

 female (A, 12-13), gives rise to the oesophagus, the stomach 

 and the digestive glands. The lower and more posterior portion 

 (r.o.) becomes differentiated into the vitellarium, ovary, oviduct 

 and uterus as indicated in the A series of figures. Beginning at 

 the point of development as indicated in the series A-C, u the 

 entodermal cells (st.~), play quite a different role in the two sexes. 

 In the male embryo (B-C, n) the cells (st.) fuse with the wall 

 of the invaginated pharynx as in the female, but do not give rise 

 to any permanent structures. Later this entodermal group of 

 cells lose their connection with the pharyngeal wall (C, 12), and 

 are gradually utilized as food. The reproductive portion (/5.) 

 gives rise to the testis and vas-deferens (C, 14). The male 

 embryo as indicated in series B, 11-15, with the exception of 

 the reproductive cells, undergoes an almost complete degenera- 

 tion. In B, ii the embryo corresponds to that of the normal 

 male (C, 1 1), but later all of the non-reproductive cells deteriorate 

 and are utilized by the embryo. When the sperm have reached 

 their maturity, the embryo is represented by a large sperm sac 

 (B, 15) within the delicate body wall or hypodermis. A portion 

 of the trochal disc and cilia often persist. 



In series C, 11-15, which represents the development of the 

 normal male as it occurs in Asplanchnia ebbesbornii, degeneration 

 occurs only in the digestive system. The early development 



