4 8 GENESIS OF MAN. 



(Synamoebid), which therefore constituted the corresponding third 

 stage of development in the anthropogenetic line. 



There must have next existed, as the fourth stage, a family of 

 creatures standing at the base of the protozoa, whose bodies con- 

 sisted of a simple, hollow sphere, the walls of which were formed 

 of a single layer of cells. These were the Planacada, and they 

 find their embryonic recapitulation in the blastosphaere stage. 

 These creatures are not yet so far extinct but that representatives 

 of them still exist in Haeckel's Mogospliacra, in Synura, and in 

 other marine and fresh-water forms. 



The gastrula-form of embryonic development, barely traceable 

 in the higher vertebrates, but common to both Amphioxus and 

 Ascidiae, as well as to many lower forms, is all there is to warrant 

 the assumption of a class of beings once peopling the waters of the 

 globe, whose bodies consisted of a simple sack, open at one end, 

 and formed of two cellular layers. These were the interesting 

 Gastraeada, which have given to all the forms that have descended 

 from them the warp and woof of all their tissues, the primary ger- 

 minative layers. They must have developed directly out of the 

 Planacada, and form the fifth stage in the descent of man. 



Ontogenesis •next points, as a sixth stage, to an extinct race of 

 primordial worms, Archelminthes, which originated from the Gas- 

 traeada by the formation of an intermediary germinative layer, 

 from which the two inner secondary layers eventually differen- 

 tiated. These creatures belonged to the lowest sub-division of the 

 worms, the Acoelomi, which, as their name implies, possess no cav- 

 ity of the body {coelom) distinct from the sack-like stomach. They 

 are also without any vascular system, heart, or blood, but manifest 

 the first traces of the formation of a nervous system, the simplest 

 organs of sense, and rudiments of secretive and reproductive 

 organs. The typical representatives of the Archelminthes are the 

 Turbcllaria, but they also closely resembled the parasitic Trema- 

 toda and Cestoda, which belong to the group Acoelomi. Thus is 

 man connected by blood relationship with the loathsome tape- 

 worm that infests his stomach ! 



Out of the Acoelomi were developed the Coelomati, which, still 

 low in the scale, nevertheless possess a distinct coelom. The now 

 extinct race which effected this transition have been called the 

 Scolecida, and form the seventh stage of anthropogenetic develop- 



