466 



Report of the State Geologist. 



a <^ / 



Fig. 29. AlcTjonella fungosa, showing the development of a free embryo, a, Spermatozoa ;"&, A 

 group of ova ; c, A single ovum, much enlarged ; cl, Showing segmentation and central cavity ; 

 c, Showing ovum developed into an oval ciliated sac ;/, Showing rudiment of polyp ; g, Polyp isolated 

 from the cell and further enlarged ; h, Polyp more advanced ; i, An embryo containing two polyps; 

 k, the same more advanced ; I, A still more advanced stage. 



A little later (fig. 4) a central cavity is seen, and the vitelline 

 spheres are arranged in a radiating manner around the center. 

 Figure 5 shows the progressive thickening of the egg with an 

 enlargement of its central cavity ; the embryo becoming elon- 

 gated and of oval form. Figure 6 shows the blastula stage well 

 formed. The central cavity is more spacious and the cells more 

 clearly radiatingly disposed. The gastrula stage shows the 

 invagination of the gastrula which here follows the typical 



