58 THE EVOLUTION OF MAN. 



Fig. 171. — Gi miination of a coral {Munoxenia Darwivii): A,n\oveTT^^Ti i 

 li, pareut-cell (cytula); C, two cleavage-cells; D, four cleavage-cells ; R, 

 mulberry-germ (vinrida) ; F, vesicular germ (hlastula) ; G, vesicular gorm 

 in section ; H, infolded vesicular germ in section ; /, gastrula in longitu- 

 dinal section; K, gastrula, or cup-germ, seen from the outside. 



kindred cells which originated through division remained 

 united. The advantages which these first cell-societies had 

 ill the stru^ixle for existence over the solitary hermit cell 

 must have favoured their progi-ession, and have encouraged 

 further development. Yet even at the present time several 

 genera of Primitive Animals live in the sea and in fresli 

 water, and permanently represent these primitive cell- 

 communities in their simplest form. Such, for instance, art 

 several species of Cystopkrys described by Archer, the 

 Rhizopods described by Richaid Hertwig under the name 

 of Mlcrogromia socialls, and the LahyrinthulcE which were 

 discovered by Cienkowski ; formless masses of homogeneous 

 and quite simple cells.^^^ 



In order to recognize the ancestors of the human races 

 which developed first phylogenetically from the Syn- 

 auMjeba, we need only continue to trace the ontogenetic 

 modification of the Amphioxus-morula in the next stages. 

 The first thing noticed is that a watery fluid collects within 

 the solid globular cell-mass, and the cells are forced 

 together and driven out to the periphery of the body 

 (Fig. 171, F,G; Plate X. Fig. 9). The solid mulberry-germ 

 thus changes into a simple hollow globe, the wall of which 

 is formed of a single cell-stratum. This cell-stratum v,'e 

 called the germ-membrane (blast oderma), and the hollow 

 ^•lobe the o-erm -membrane vesicle ( blast ala, or blasto- 

 sphcera). 



