SUMMARY. 433 



place in nature,* cannot, we believe, be made too prominent. If the Theory 

 of Descent is correct as a whole, then the theory that man has developed 

 from lower Vertebrates is simply an unavoidable deductive conclusion from 

 that general inductive law. Hence, all farther discoveries which may in 

 future enrich our knowledge of the phyletic development of man, can only 

 be confirmative of special points of that deduction, which restg on the 

 broadest inductive basis." — Generelle Morphologic (1866). 



As we have now traversed the wonderful territory of 

 the history of human development, and learned its most 

 important parts, it seems appropriate that, at the close of 

 our travels, we should look back on the road behind us, 

 and, on the other hand, glance forward along the further 

 path of knowledge into which our road will lead in future. 

 We started from the simplest facts of the history of man's 

 individual development; ontogenetic facts which can, at 

 any moment, be shown and established by microscopic or 

 anatomic research. The first and most important of these 

 ontogenetic facts is, that every man, like every other 

 animal, is at the commencement of his individual existence, 

 a simple cell. This egg-cell exhibits precisely the same 

 structure and mode of origin as that of any other Mammal. 

 From this cell proceeds, by repeated division, a many-celled 

 body, the mulberry-germ (morula); this changes into a 

 cup-germ (gastrula), and this, again, into an intestinal 

 germ-vesicle (gastrocy§tis). The two distinct cell-strata 

 which compose its wall are the two primary germ- 

 layers ; the skin-layer (exoderma) and the intestinal layer 

 (entoderma). This double-layered germ-form is the onto- 

 genetic reproduction of that extremely important phylo- 

 genetic parent-form of all Intestinal Animals, to which we 

 have given the name Gastrsea. 



As the human germ, like that of other Intestinal Animals, 



