PROGENITORS OF MAN, 281 
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 all 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 larvee (Planzea, 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. 
FirtuH Srace: Primeval Stomach Animals (Gastreada). 
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 primeval animal of 
the same structure, and this we have named primeval 
stomach animal, or Gastrza (pp. 127, 128). These 
Gastreeada must have existed during the older Primordial 
period, and they must have also included the ancestors of 
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