PEOGENITORS OF MAN. 28 1 



the Lanceolate Animals, or Amphioxus, there first develops 

 out of the Morula (Frontispiece, Fig. 3) a ciliated larva 

 (planula). Those cells, lying on the surface of the homo- 

 geneous mass of cells, extend hair-like processes, or fringes 

 of hairs, which by striking against the water keep the 

 whole body rotating. The round many-celled body thus 

 becomes differentiated, in that the external cells covered 

 with cilia differ from the non-ciliated internal cells. 

 (Frontispiece, Fig. 4). In Man and in aU other Vertebrate 

 animals (with the exception of the Amphioxus), as well 

 as in all Arthropoda, this stage of the ciliated larva has been 

 lost, in the course of time, by abbreviated inheritance. 

 There must, however, have existed ancestors of Man in the 

 early Primordial period which possessed the form value of 

 these ciliated larvae (Plansea, p. 125). A certain proof of 

 this is furnished by the Amphioxus, which is on the one 

 hand related by blood to Man, but on the other has retained 

 down to the present day the stage of the planula. 



Fifth Stage : Primaeval Stomach Animals (Gastraeada) . 



In the course of the individual development of Am- 

 phioxus, as well as in the most different lower animals, 

 there first arises out of the planula the extremely important 

 form of larva which we have named . stomach larva, or 

 gastrula (p. 126 ; Frontispiece, Fig. 5, 6). According to the 

 fundamental law of biogeny this gastrula proves the former 

 existence of an independent form of primaeval animal of 

 the same structure, and this we have named primaeval 

 stomach animal, or Gastraea (pp. 127, 128). These 

 Gastraeada must have existed during the older Primordial 

 period, and they must have also included the ancestors of 



