BY R. VON LENDENFELD, PH.D. 323 



Amoeboid wandering cells, very much like amoebae with lobate 

 Pseudopodia are common in all parts of the Sponges, their function 

 is merely to serve as vehicles of food and oxydized substances, as 

 we shall see in the chapter on Physiology. 



Some of these cells are developed into the generative elements. 

 The form ova and Spermasacks around which an endothel-like 

 Follicle is formed by other Mesodermal cells. 



The sperma forming cells are of a peculiar kind (Polejaeff Sper- 

 matogenese von Sycandra raphanus) with a Protoplasm which 

 refracts the light in a greater degree than any other cells. By 

 continuous partition of this cell, finally a heap of small cells are 

 produced, which produce a tail and turn into Spermatozoa. These 

 always consist of a narrow, sharp, lance-point-shaped head and a 

 long tail. The proximal part of the tail is immovable and thick, 

 it tapers abruptly to the thin moving distal part. 



The ova are not produced in the same manner as the Sperma- 

 tozoa, it is probable that each amseboid cell only produces one 

 ovum. (von. Lendenfeld. Neue Aplysinidse.) 



All these amoeboid cells, the wandering cells always, and the 

 sexual cells in their young stages creep about very actively in the 

 ground substance of the Mesoderm. 



Similar amoeboid cells are known in the Medusae, but of course 

 the sexual products do not take their origin from these in the 

 higher Ccelenterata. 



III. — Embryology. 



The development of the Sponges, and particularly the first 

 stages, can easily be studied, because the embryos remain within 

 the mother until they have attained a pretty high degree of 

 development. In the shape of oval ciliated Gastrulse they 

 leave the mother and swim about in the sea water for a short 

 time. They then fix themselves to anything suitable and grow 

 out into the Sponge. This latter part of the Ontogenesis is the 

 most difficult to investigate, it is only of late that F. E, Shulze, 

 Keller, and Marshall have succeeded in attaining an insight into 

 the changes which the ciliated and free swimming embryo under- 

 goes before it produces the Sponge. 



