STUDIES ON THE COMPARATIVE ANATOMY OF SPONGES. 221 



stores of nutritious matter. In Leucandra aspera and 

 Sycon raphanus . . . . the collar cell, after it has accumu- 

 lated a certain quantity of spherules in its base, splits off this 

 base by a transverse fission as a non-nucleated mass of pro- 

 toplasm, which we may term a 'plinth' (fig. 4); the plinth 

 then lies between the nucleated distal part of the cell — the 

 'column' — and the mesodermal jelly in S. raphanus, or the 

 thin basement membrane which is all that usually divides 

 the epithelia in L. aspera. I have observed in the meso- 

 derm of S. raphanus large wandering cells, which I believe 

 to be generative elements, with pseudopodia attached to these 

 plinths, aud spherules of the same character as the basal 

 spherules, both in the wandering cells and in their pseudo- 

 podia. There can be little doubt that they were feeding on 

 ths reserve stores of the collar-cells. The division into column 

 and plinth takes place as a rule at the same time in all or 

 most of the cells of a chamber. The ' columns' or distal 

 parts appear as small, columnar, nucleated cells, provided with 

 a small amount of clear protoplasm, rudimentary collars not 

 united, and flagella (fig. 4a)." Later on, in the same paper, 

 Bidder observes that he interprets the peculiar structures met 

 with by me in Grantia labyrinthica as column-and-plinth 

 chambers violently contracted in alcohol. There is certainly 

 a good deal to be said in favour of this view, and, examining 

 the structures in question in the light of Bidder's remarks, I 

 have seen in Leucandra phillipensis appearances which 

 might be taken as indicating the formation of "plinths." The 

 abundant occurrence of small nucleated cells in the mesoderm 

 which surrounds the contracted chambers, as shown in fig. 24, 

 is certainly suggestive either of the congregation of amoeboid 

 cells to feed on the collared cells, or of the collared cells or 

 segments thereof becoming amoeboid and wandering away 

 into the mesodermal jelly. The occurrence of such cells in the 

 surrounding jelly is characteristic of the contracted chambers, 

 and their small size appears to me to be an argument in favour 

 of regarding them as metamorphosed collared cells rather than 

 as ordinary amoeboid ones. 



