58 THE EVOLUTION OF MAM. 



FIG. 171. Germination of a coral (Monoxenia Dancinii): A, moneruTa ; 

 B, parent-cell (cytula); C, two cleavage-cells; D, four cleavage-cells ; L\ 

 mulberry-germ (morula) ; F, vesicular gei-m (blastula) ; G, vesicular germ 

 in section ; H, infolded vesicular germ in section ; J, 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 

 in the struggle for existence over the solitary hermit cell 

 must have favoured their progression, and have encouraged 

 further development. Yet even at the present time several 

 genera of Primitive Animals live in the sea and in fresh 

 water, and permanently represent these primitive cell- 

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

 several species of Cystophrys described by Archer, the 

 Rhizopods described by Richard Hertwig under the name 

 of Mierogromia socialis, and the Labyrinthidce which were 

 discovered by Cienkowski ; formless masses of homogeneous- 

 and quite simple cells. 140 



In order to recognize the ancestors of the human races- 

 which developed first phylogenetically from the Syn- 

 amceba, 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 we 

 called the germ-membrane (blastoderma*), and the hollow 

 globe the germ-membrane vesicle (blastula, or blasto- 

 spJtcera). 



