EARLY DEVELOPMENT OF GRANTIA COMPRESSA. 269 



go intensely brown or black. Such large apparently non-mitochondrial 

 granules are possibly yolky bodies partly formed of a dense proteid basis, 

 whence their histocbemical behaviour. 



Presumably these nutrient granules are the direct descendants of those 

 yolk-spheres which one rinds in the histocytes or flagellated cells of the 

 amphiblastula larva (PI. 23. tig. 28, Y, and PL 23. fig. 32, Y). Nevertheless, 

 such laroe nutrient granules of the flagellated collar-cell of Grantia are not 

 quite like the yolk-spheres of the embryonic histocj'te ; the former granule 

 has a heavier proteid basis, which takes crystal violet and hematoxylin, as 

 well as occasional impregnation in silver nitrate. At one stage of this work 

 I did not feel sure that the nutrient granule and the mitochondrium of the 

 collar-cell could be distinguished from each other, but some of my later 

 preparations appeared conclusive. Probably the most convincing evidence 

 is acquired by examining two sets of preparations, one by the Kopsch, 

 the other by the Flemming-without-acetic method (4). In the former, 

 yolk or nutrient bodies are markedly demonstrated, in the latter such bodies 

 are not properly shown, while mitochondria stain densely. 



8. Amwboid Cell-elements of Grantia. 



Besides the ordinary flagellated cells in situ lining the gastral cavities, one 

 finds many wandering mesogleal cells whose origin can be traced to the 

 flagellated cells, as depicted in PI. 22. fig. 24 (see also PL 19. fig. 7). 



Such amoeboid cells are the commonest elements of the mesoglea and very 

 probably give rise to both spermatozoa and ova. In addition to the ordinary 

 amoeboid cells, whose cytoplasmic inclusions much resemble those of the 

 collar-cells, one occasionally finds small cells loaded with mitochondria. 

 These granular cells are very distinctive, and examples of them are seen at 

 GAM in PL 21. fig. 21 and PL 22. fig. 23. Such cells contain in their 

 cytoplasm a large number oE mitochondrial granules, and very little of any 

 nutrient yolk-spheres. They are probably formed from the histocytes 

 during late larval and early pupal life, as shown in PI. 23. fig. 28, GAM, 

 and in PL 23, fig. 30. I do not intend here to enter into the questions 

 surrounding other elements of the sponge, but the two kinds of cells above- 

 mentioned are the only sorts of amoeboid cells which have been met with by 

 me, and which could give rise to gametes. 



That the germ-cells may arise from the ordinary wandering mesogleal 

 cell (PL 19. fig. 7) is very probable, but the smaller and more densely 

 granular cells are less common — so rare, in fact, that one could not believe 

 that they provide a large quantity of germ-cells, if any at all. 



