EARLY DEVELOPMENT OF GRANTIA COMPKESSA, 273 



In PL 19. fig. 5 is depicted a part of a hermaphrodite individual 

 showing one gastral cavitry, on the left an oocyte about to be fertilized, and 

 on the right a nest of spermatids (SPT), enclosed by their nurse-cells (NSC). 

 The hitter are pale cells, cubical, and contain faint granulations ; they are 

 not ciliated and the epithelium they form may be partly interrupted by 

 absence of cells at any one side. 



The spermatids lie inside the cavity of the nurse-cell chamber (SPA), and 

 their tails can easily be seen. 



In my material I was in addition able to recognise larger cells also 

 enclosed by a nurse-cell chamber — these I believe to be spermatocytes, as 

 they are of the expected size. 



These aggregations of sperm-cells probably arise at a certain period of the 

 year from amoeboid elements of the mesoglea, and the nurse-chamber would 

 be formed subsequent to the inception of spermatogenesis. 



14. General Description of the Inclusions of the Cytoplasm in Oogenesis. 



The young oocyte of Grantia contains the usual three cateoories of 

 cytoplasmic granules or bodies, i.e. yolk-spheres, mitochondria, and Golgi 

 apparatus. In PI. 19. fig. 2 is a young oocyte containing three Golgi elements 

 (GAO), with yolk ;md mitochondria stained yellowish. The apparatus is 

 like that of the flagellated cells, being formed of an inner protoplasmic 

 (archoplasmic) area, surrounded by a peripheral rind of Golgi material. 

 My Kopsch preparations were not suitable to study the Golgi apparatus in 

 all stages, because those which were successful did not contain oocytes older 

 than that drawn in PI. 19. fig. 2. 



The mitochondria I worked out fully : they are the " chromidia " of 

 Jorgensen. Without clouding this present section with controversy with 

 regard to the origin of the germ-cells, it can be stated that those cells (in 

 fact, all cells of the sponge) from which the gametes ultimately arise 

 contain mitochondria in their earliest stages. There can then be no 

 question as to the origin of the sponge mitochondria from chromatin. 

 The mitochondria in the young oocyte (PI. 19. fig. 8) may be extremely 

 large and coarse, and they lie in the endoplasmic region. As the oocyte 

 grows larger, the mitochondria become more numerous and generally smaller 

 at first, but later they may grow very large and dense. As soon as the 

 oocyte has grown so large that the crowding of the granules is less marked, 

 vacuoles begin to appear in the endoplasm. 



The yolk in the Grantia compressa oocyte cannot be demonstrated properly 

 by short fixation in chrome-osmium, as is suitable for mitochondria. The 

 best method for demonstrating yolk is the unmodified Kopsch (7). 



In PI. 19. fig. 9 is an oocyte just before fertilization, showing the mito- 

 chondria (black) and the very fine numerous yolk-granules as lightly stained 

 bodies. The yolk-bodies of the egg of Grantia are so delicate that only 



