^^ THE NEW EVOLUTION '^'^^^ 



None of the animal types in this second series of four can be 

 assumed to have any direct connection with any of the flatworms 

 or roundworms, nor can it be shown that they have any connec- 

 tion with each other. Their development, however, where it is 

 known, shows that the very early stages resemble the correspond- 

 ing stages of the coelenterates, but that they branch off from the 

 regular geometrical line in such a way as to lead to the formation 

 of completely bilateral larvae and subsequently adults in which 

 the broader structural features may be interpreted as combining 

 those of two separate groups of Vermiformes. 



As they depart from the coelenterate line of development in 

 very early larval stages, their origin was presumably simultane- 

 ous with that of the coelenterates and the Vermiformes and had 

 its inception in the different behavior of the gastrula. For in- 

 stance, while the very young jointed tapeworm embryo develops 

 in such a way as to produce a sharply jointed and semicolonial 

 animal, and the fluke embryo during its growth undergoes exten- 

 sive internal budding, the young embryo of the jointed worms or 

 annelids in its development combines both external segmenta- 

 tion and internal budding. 



Within this second series of four animal types there is another 

 series of four which bears the same relation to the second series 

 that the second series does to the first. 



The third series of four animal types includes : 



I. The polyzoans, which are colonial, or at least primarily 

 colonial, and not at all, or only very imperfectly coelomate, fall- 

 ing between the rotifers and the graptolites. 



-L. The arthropods, with a segmented body like that of the 

 annelids, but divided into two or three units showing division of 

 labor (in the insects one, the head, controlling and directing, 

 another, the thorax, bearing the legs and wings and therefore 

 locomotor, and the third, the abdomen, containing the digestive, 

 reproductive and other organs) after the graptolite or polyzoan 

 fashion, with a poorly developed coelom, with abundant traces 

 of asexual reproduction (polyembryony, parthenogenesis, frag- 

 mentation of larvae, etc.), with a marked tendency to form (as 

 in the ants) polyzoan-like colonies with division of labor among 

 the (independent) units, and sometimes (as in Thompsonia) even 

 forming dendritic colonies. 



3. The mollusks, always solitary, like the sipunculids, with 



