42 CM. CHILD 



are more highly speciahzed than the basal or posterior and dorso- 

 posterior, and it is suggested that the origin of the body-region 

 with its high developmental potentialities and capacity for 

 long-continued growth from the dorso-posterior region of the 

 egg is connected with these differences. This region undergoes 

 a greater degree of rejuvenescence during early development 

 than the other egg-regions and gives rise to the posterior growing 

 region. This interpretation brings the peculiar course of anne- 

 lid development into relation with the axial gradients and with 

 the development of other forms. 



6. The developmental gradient decreasing in rate anteriorly 

 from the posterior growing region, which is characteristic of the 

 whole segmental region in the three-segment stage, is replaced, 

 after metamorphosis, in the more anterior segments of Areni- 

 cola and undoubtedly also of other forms by a gradient in the 

 opposite direction, which is an indicator of the progressive nervous 

 integration of the segments and the dominance of the head-region 

 and may be called the integrative gradient. This integrative 

 gradient coincides In direction with the primary, apico-basal 

 gradient and is, physiologically speaking, the final developmental 

 consequence of the existence of the primary gradient. 



7. Some differences in size relations between eggs and larvae 

 and larval proportions in the different species are shown to be 

 associated with the metabolic relations of different regions and 

 the nutritive supply of the egg. 



