229 



The changes in the position of the nucleus in C lath ri nid a e 

 acquire a still greater interest when compared with the state of things 

 found in the embryonic development. In the larvae of both Clathri- 

 nidae and Leu cesoie niidae, possibly in the larvae of all calcareous 

 sponges, the flagella of the superflcially placed flagellated cells, that is 

 to say of those cells which later becomes the collar-cells, are in all 

 cases in direct continuity with the pear- shaped nuclei (figg. 4 and 5 ; 

 see also Hammer, Taf. XXV). In other words, the condition found 

 in Lcucosolenia and Sì/coìì is the larval condition, which these forms 

 retain unaltered in the adult, but which in (ylathrinidae is lost com- 



4. 5 6 



Fig. 1. Collar-cells of Claihrina coriacea in the fully-expanded condition of the 



sponge, showing the cells with relatively broad bodies and very long collars. 



Fig. 2. Collar-cells of the same species in the partially contracted condition, with 



longer bodies and shortened collars. 



Fig. 3. Collar-cells of Leucosolenia complicata. 



Fig. 4. Flagellated cells (future collar-cellsi of the lam'a of Leucosolenia variabilis. 



Fig. 5. Flagellated cells of the larva of Clathrina bianca. 



Fig. 6. Collar-cells lining the gastral cavity of the pupa of Clathrina bianca on the 



7th day of fixation, shortly before the formation of the osculum, showing various 



positions of the nucleus in the cell; the collars are not yet formed. All figures 



magnified 1000 diameters, the outlines drawn with the camera lucida. 



pletely during the development. I have been able to find all stages of 

 the change in my sections of Clathrina bianca in its postlarval stages. 

 In sections of pupae shortly before the formation of the osculum, and 

 before the collars grow out from the collar-cells, it is seen that the re- 

 ation of the nucleus to the flagellum, and its position in the cell, varies 



