Nos. 618-619] THE ROLE OF REPRODUCTION 277 



duction in the narrow sense is common in Protozoa, Porif- 

 era, Coelenterata and Platyhelminthes, and is sporadic in 

 Molluscoida, Annulata, Arthropoda and Chordata. If 

 fragmentation and regeneration be included, Echinoder- 

 mata and possibly Neinathelminthes are added. If 

 parthenogenesis is included, Trochelminthes is admitted. 

 Thus only the Mollusca have no form of asexual reproduc- 

 tion, and zoologists would hardly feel safe in maintaining 

 its absence there since the life history of so many forms is 

 unknown. This being the case, one must admit that 

 asexual reproduction has been found satisfactory for 

 most of the great groups of animals as far as actual 

 multiplication is concerned. For other reasons, however, 

 it evidently did not fulfill all requirements, since sexual 

 reproduction is established in every phylum. Further, 

 omitting the Protozoa in which it is difficult to decide such 

 sexual differences, gonochorism is present everywhere 

 except in the Porifera, and hermaphroditism everywhere 

 except in the Trochelminthes, although in Nemathel- 

 minthes, Echinodermata and Arthropoda it is rare. 



Now if our conclusions regarding the true role played 

 by sex in evolution are correct, hermaphroditism is a 

 secondary and not a primitive phenomenon. In this we 

 follow Delage, Montgomery and Caullery rather than the 

 majority of zoologists. We believe it to be the only 

 logical view in spite of the fact that the Porifera, usually 

 considered so unspecialized, are all hermaphroditic. 

 Perhaps the Porifera are farther along in specialization 

 than is admitted, for to find the substance nearest chemi- 

 cally to the so-called skeleton of the sponges one must 

 turn to the arthropods (the product of the spinning glands 

 of certain insects). Hermaphroditism, therefore, as in 

 plants, is from this viewpoint a regression. And as in 

 plants it was not found adequate. In giving up diecism 

 for monecism, something was lost, and this something had 

 to be regained by further specialization. Hence, even as 

 in the vegetable kingdom one finds the essential feature of 

 bisexuality, mechanisms providing for mixtures of dif- 



