92 MARINE BIOLOGICAL LABORATORY. 



tain of the superficial cells became amoeboid and mi- 

 grated into the interior of the colony just as we find 

 them doing to-day in Pivtospongia, and that, in addition, 

 certain other cells divided transversely, one of the cells 

 so formed passing into the interior, while the more 

 peripheral one retained its position at the surface. . . . 

 While transverse division became predominant in some 

 forms, longitudinal division and consequently the immi- 

 gration of superficial cells prevailed in others. In this 

 manner from mixed delamination, primary delamination 

 branched off on the one hand, and multipolar immigra- 

 tion on the other." 



Is it necessary though to assume that this " mixed 

 delamination," i.e. a mixture of delamination and immi- 

 gration, was characteristic of the ancestral flagellate 

 colony.? May we not claim that immigration is the 

 more primitive method, and that delamination has been 

 secondarily acquired after the group Metazoa had been 

 well established "^ There is evidence in the colonial 

 Protozoa in favor of such a view ; as, for instance, in 

 Protospongia in which cells, originally seated superfi- 

 cially in the jelly in which the individuals of the colony 

 are imbedded, pass to the centre, losing their flagella 

 and collars, and becoming, according to Saville Kent, 

 reproductive. Volvox again, when mature, is a hollow 

 sphere with reproductive cells lying freely in the central 

 cavity ; these cells were originally at the surface, but, 

 losing their flagella, they migrated to the centre. The 

 same process too is found in the sponges in Ascetta, 

 and Metschnikoff has demonstrated its prevalence over 

 delamination in the metagenetic Hydromedusae. 



If this idea be accepted, however, how can delamina- 



