204 



ZOOLOGY 



SECT. 



no, 



same sex face one another. It will be seen that the reproductive 

 products have, as in Scyphozoa and Actinozoa, the position of 

 endoderm-cells : whether they are developed, in the first instance, 



from that layer is uncertain. 

 When ripe the ova and 

 sperms are discharged into 

 the canals, make their way 

 to the infundibulum, thence 

 to the stomoda3um,and finally 

 escape by the mouth. Im- 

 pregnation takes place in the 

 water. 



Development. The pro- 

 cess of development has been 

 traced in several genera 

 closely allied to Hormiphora, 

 so that there is every reason 

 to believe that, in all essen- 

 tial particulars, the following description will apply to that genus. 

 The egg (Fig. 150) consists of an outer layer of protoplasm (plsm.) 

 containing the nucleus (nu.), and of an internal mass of a frothy 

 or vacuolated nature (yk.) : the vacuoles contain a homogeneous 

 substance which serves as a store of nutriment to the growing 

 embryo, and apparently corresponds with the yolk which we shall 

 find to occur in a large proportion of animal eggs. Enclosing 

 the egg is a thin vitelline membrane (v.m.), separated by a consider- 

 able space, filled with a clear jelly, from the protoplasm. 



After impregnation the oosperm segments, but the details of 

 the process are very different from those we are familiar with in 



FIG. 150. Ovum of Lampetia. 

 plsm. protoplasm ; r. TO. 

 yk. yolk. (After Chun.) 



in. nucleus 



.. plsm. protoplasm ; r. TO" vitelline membrane 

 Ik. 





FIG. 151. Segmentation of the oosperm in Ctenophora. mg. megameres ; mi. micromeres ; plsm. 

 protoplasm ; yk. yolk. (Modified from Korschelt and'Heider.) 



the other Ccelenterata. The protoplasmic layer accumulates on 

 the side which will become dorsal, and the oosperm divides along 



