6o 



THE EVOLUTION OF MAN. 



Various kinds of Primitive Animals, which yet exist 

 both in the sea and in fresh water, are formed essentially 

 like the blastula, and which, in a certain sense, may be con- 

 sidered as permanent or persistent blastula-forins, hollow 

 vesicles, the wall of which is formed of a single stratum of 

 ciliated homogeneous cells. These Planseads, or Blastseads, 

 as they may be called, are formed in the very mixed society 

 of the Flagellatae, especially the Volvoces (for instance, 

 Synura). I noticed in September, 1869, on the Island Gis-Oe, 

 on the coast of Norway, another very interesting form, which 

 I named Magosphcera planula (Figs. 172, 173). The fully 

 developed body of this forms a globular vesicle, the wall of 

 which is composed of from thirty to forty vibratory homo- 

 geneous cells, and which swims about freely in the sea. After 



Fig. 172. — The Norwegian Flimmer-ball (Magosphcera planula), swim- 

 ming by means of its vibratile fringes ; seen from the surface. 



Fig. 173. — The same, in section. The pear-shaped cells are seen bound 

 together in the centre of the gelatinous sphere by a thread-like process. 

 Each cell contains both a kernel and a contractile vesicle. 



