62 THE RIDDLE OF THE UNIVERSE. 



VII. — This phylogenetic conclusion, based on the 

 comparison of ontogenetic facts, is confirmed by the 

 circumstance that there are several of these gastreeades 

 still in existence (gastr^maria, cyemaria, physemaria, 

 etc.), and also some ancient forms of other animal 

 groups whose organisation is very little higher (the 

 olynthus of the sponges, the hydra, or common fresh- 

 water polyp, of the cnidaria, the convoluta and 

 other cryptocsela, or worms of the simplest type, of 

 the platodes). 



VIII. — In the further development of the various 

 tissue-forming animals from the gastrula we have to 

 distinguish two principal groups. The earlier and 

 loicer types (the coelcnteria or accelomia) have no body 

 cavity, no vent, and no blood ; such is the case with 

 the gastrseades, sponges, cnidaria, and platodes. The 

 later and higher types (the calomaria or bilateria), 

 on the other hand, have a true body cavity, and 

 generally blood and a vent; to these we must refer 

 the worms and the higher types of animals which 

 were evolved from these later on, the echinodermata, 

 mollusca, articulata, tunicata, and vertebrata. 



Those are the main points of my " gastrsea theory "; 

 I have since enlarged the first sketch of it (given in 

 1872), and have endeavoured to substantiate it in 

 a series of " Studies of the gastrsea theory " (1873-84). 

 Although it was almost universally rejected at first, 

 and fiercely combated for ten years by many authori- 

 ties, it is now (and has been for the last fifteen years) 

 accepted by nearly all my colleagues. Let us now 

 see what far-reaching consequences follow from it, 

 and from the evolution of the germ, especially with 

 regard to our great question, "the place of man in 

 nature." 



