1892.] 



Note on Excretion in Sponges. 



477 



slightly darker than the surrounding protoplasm, and are generally 

 stained to a greater or less degree by hematoxylin. 



Their most important reaction, in which they differ alike from the 

 nuclei and the excretory granules, is the characteristically staining 

 during life deeply and immediately with Bismarck-brown. This was 

 observed in Ascetta primordialis, Ascaltis cerebrum, Ascandra Lieber- 

 huhni, and Sycon raphanus ; after keeping Sycon raphanus some days 

 alive, but in unfavourable circumstances, the spherules, though still 

 visible, did not stain more than the surrounding protoplasm. 



I believe these basal spherules to be stores of nutritious matter. 

 In Leucandra aspera and Sycon raphanus (I have once observed indi- 

 cations in Ascetta primordialis) 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 protoplasm, which 

 we may term a " plinth " (fig. 4) ; the plinth then lies between the 



External Surface 



~FiG. 3. — Section through the greater part of the length of an afferent pore in 

 Ascetta clathrus. The nuclei are shown, and endodermal vacuoles, two of 

 which contain amorphous matter. The spaces left by spicules in the inter- 

 cellular jelly are not shown here or in Fig. 2. Diameter of pore 6'5/x. Osnuc 

 acid and Mayer's carmine. 



nucleated distal part of the cell — the " column " — and the mesodermal 

 jelly in 8. raphanus, or the thin basement membrane which is all that 

 usually divides two epithelia in L. aspera. I have observed in the 

 mesoderm of S. raphanus large wandering cells, which I believe to be 

 generative elements, with pseudopodia attached to these plinths, and 

 spherules of the same character as the basal spherules both in the 

 wandering cells and in their pseudopodia ; there can be little doubt 

 that they were feeding on the 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). 



2 x 2 



