STRUCTURE OF THE LARVA OF SPONGILLA LAOUSTRTS. 413 



guished from the yolk bodies only by tlieir affinity for a differ- 

 entiating stain.' The nuclei then pass during this stage 

 through a series of changes in rapid succession, and are there- 

 fore not constant in structure. The yolk bodies also change 

 from stage to stage, owing to their being used up in the forma- 

 tion of living protoplasm. These changes, both in the nuclei 

 and in the yolk bodies, render interpretation of the phenomena 

 observed a most difficult task. It is evident, however, from the 

 characters of the chambers represented in fig. 28, that the 

 flagellated cells give rise to a series of chambers in the pupa 

 derived from a larva of type C, in the same way as they do in 

 the one of type D. The former statement is far more difficult 

 to prove than the latter, owing to the complication brought 

 about by the presence of a number of chambers derived from 

 the cells of the inner mass in type C, and consequently in the 

 pupa derived from that type of larva. But the presence of yolk 

 bodies in the pupa on the one hand, and of flagellated cells 

 on the other, suffice to explain the conflicting statements 

 which have been made by various observers, and to reconcile 

 them in the following manner. Some of the bodies contained 

 in the plasmodial aggregation, namely, the yolk granules, 

 become used up and disintegrate, whilst others of a different 

 nature emancipate themselves and give rise to the nuclei of the 

 collar-cells. 



The question of the formation of the flattened epithelium 

 from the cells with granular nuclei has been incidentally men- 

 tioned, but it must be described here at a greater length from 

 the point of view of the structure of the pupa derived from 

 the larva described as type C. The flattened epithelium of the 

 lower surface forms much more quickly than that of the upper 

 surface, in correspondence with the different rate at which the 

 flagellated layer disappears from these surfaces. The difference 

 in question is brought out very sharply in fig. 29, while in 



• With carmine and bleu de Lyon the nuclei are stained red, while the yolk 

 bodies are stained blue. This reaction is difficult to bring about owing to the 

 thickness of the nuclear membrane, which stains blue in the same way as the 

 yolk bodies. 



