404 ElCHAliD EVANS. 



In an individual produced by the metamorphosis of type C, 

 the plasniodial aggregations will of necessity be mixed up with 

 the flagellated chambers derived from the cell groups. 



Since individuals occur with neither chambers nor free cells 

 capable of forming chambers, but with the interior full of 

 plasniodial aggregations surrounded by cells with granular 

 nuclei at the surfaces, the important question of the origin of 

 the cells which later on become the collar-cells of the flagel- 

 lated chambers forces itself upon us. Are they developed 

 anew from the cells with vesicular nuclei, or do the flagel- 

 lated cells — no longer flagellated, it is true — separate themselves 

 from the plasniodial aggregations into the composition of 

 which they have entered, in order to develop into collar-cells? 

 If the latter be the actual course of the development, it would 

 furnish a further proof of the homology of the flagellated 

 cells with the constituent cells of the " cell groups," which are 

 characteristic of types B and C, and which in the latter have 

 developed into flagellated chambers. To answer this question 

 it is necessary to trace further the morphological changes 

 undergone by that constituent of the plasniodial aggregations 

 which owes its origin to the immigration of the surface layer 

 of cells in the larva. 



The small nuclei of the flagellated cells which have already 

 been traced through a series of changes, leading them to 

 acquire a structure almost indistinguishable from that of the 

 yolk bodies, now embark upon a similar series of transforma- 

 tions, but in the reverse order, as the result of which they 

 revert to a condition slightly different from that which they 

 presented as the flagellated locomotor layer at the surface of 

 the larva. 



The small nuclei — that is the nuclei of the cells which were 

 once flagellated — in the plasmodial aggregations commence 

 this series of changes by increasing slightly in size, simul- 

 taneously with some internal changes in disposition of the 

 chromatin and nuclear reticulum. At one stage they appear 

 as oval masses, uniformly coloured in stained sections, but 

 now the chromatin becomes looser and aggregated into small 



