103 



Development. Lieberkiihn made the astonishing discovery, con- 

 firmed by Hseckel, that sponges were really hermaphrodite animals 

 reproducing by eggs and sperm cells developed Ft*. 46. 

 in the same individual sponge. Hseckel showed 

 that they were probably developed from the inner 

 (endodermal) layer of cells forming the body, 

 being simply modifications of these endodermal 

 cells, much as the eggs of the higher animals are 

 mod'fied epithelial cells. Fig. 47, from Haackel, 

 shows one of these cells (of Sycortes quadrangu- 

 lata) with several spermatozoa mingling their 

 protoplasmic contents with the protoplasm of the 

 egg itself. 



The endodermal cell transforms into an egg, 

 according to Hseckel, in the following manner. 

 At first provided with a "collar" and flagellum «3«j \ 

 much as in the Codosiga figured on page 42, it Schmidt.' 

 begins to draw these in until they disappear ; then a nucleus (nu- 

 cleolmus) appears within the nucleolus of the cell. The egg soon 

 becomes detached from the body wall, and Fig. 47. 



th^-r, it lK-in, to tl !] :\;\\u^n t ,,,;, llfre 

 splitting into two, After Hasckfii. 

 ., nucleolinated cells (Fig 48, total seg- 

 mentation of eggs of Halisarca), 

 the process being exactly as in 

 the eggs of nearly all the higher 

 animals including man. This 

 stage of segmentation, like the 

 mulberry mass of the egg after 

 segmentation in the higher ani- 

 la stage (from its likeness to the mul- 

 , after Carter). The cells of the 



