EARLY DEVELOPMENT OF GRANTTA COMPRESSA. 295 



acid; K. = Kopsch; I.H. = Heidenhain's Iron Alum Hematoxylin; Ch.K. = Ckampy-Kull ; 

 Alt,=Altmann's stain. 



All figures have been drawn with camera lucida by means of a T V semi-apochromatie 

 oil immersion and compensating- eye-pieces. Figs. 2, 3, 5 a, 6, 7. 8, 9, 11-22, and 29-31, 

 and 33 were drawn with an 18 compensating eye-piece. Figs. 5 and 23-28 and 32 with an 

 8 compensating eye-piece. Figs. 1 and 4 were not drawn to scale. Fig. 10 was drawn 

 with a 12 compensating eye-piece. 



The Plates have been reduced, but a scale is given at the side of Plate 21, which 

 applies to all fig's, drawn with an 18 compensating eye-piece. Scale to fig. 10 is alongside 

 the drawing. Scale to all the figs, on Plate 22 is given at the left side, excepting to 

 figs. 29-31 and 33, whose scale is found on the right. 



While PI. 19. figs. 1, 4, and 9 are drawn with the camera lucida, they are a combination, 

 of both Kopsch, Champy-Kull, and Iron Alum Hematoxylin preparations. The same 

 applies to PI. 20. figs. 13, 14, and PI. 21. figs. 18, 22. Every care has been taken, however, 

 to see that the strictest accuracy has been preserved, corresponding stages in Champy-Kull 

 or F.W.A. and I.H. being united with those in Kopsch preparations. All the other 

 figures are drawn from one preparation only. In each case the arrow points to the nearest 

 (/astral cavity (compare PL 19. fig. 5 to illustrate this). 



Plate 19. 



Fig. 1 A & B. Two collar-cells or choanocytes drawn and combined from two preparations, 

 one by Kopsch's method (fig. 2), the other by chrome-osmium and Iron 

 Hematoxylin. The smaller granules are mitochondria, the larger yolk-spheres 

 (reserve granules). In fig. 1 A, the nucleus lies on the outer part of the cell, in 

 fig. 1 B in the middle ; in each the Golgi apparatus is shown at GA ; in fig. 1 A 

 the flagelluui comes out of the latter, in fig. 1 B it passes through or to one side 

 of the Golgi apparatus, and reaches to the ceutrosome, which lies on the nucleus. 

 The collar in fig. 1 B is partly retracted and shows an outer (OT) and an inner 

 thickening (IT) ; in fig. 1 A the collar is stretched out and the thickenings are 

 not so marked. On the periphery of the cell, at PE, is a denser region of the 

 protoplasm. K. and I. H. 



Fig. 2. Row of choanocytes and a young oocyte b) r Kopsch's method. 



Fig. 3. Same, fixed in Hermaun-without-acetic acid and stained in Iron Hematoxylin. 



Fig. 4. Choanocyte by Kopsch's method, to show characteristic neck to cell (NK). This 

 consists of hyaline protoplasm. The Golgi apparatus (GA) is very clearly 

 marked, and consists of archoplasm (AS) surrounded by a peripheral layer of 

 darkly staining matter (GA). 



Fig. 5. Part of a hermaphrodite sponge which contained ripe oocytes and ripening 

 spermatids. The latter (SPT) lie in a special cavity (SPA), lined by non- 

 flagellate cells (NSC) without collars. These cells are probably formed in the 

 mesoglea. At GCAV is the gastral cavity lined by choanocytes (GE), and at 

 OTE is the oocyte showing ectoplasmic (EOT) and endoplasmic (END) regions; 

 this oocyte is just about to be fertilized (S). Note the tails (axial filaments) of 

 the spermatids. 



Fig. 5 a. A group of three spermatids drawn at a high power showing nucleus with karyo- 

 some, the centrosome, and the axial filament. The mitochondrial substance was 

 washed away. Cajal. 



Fig. 6. Spermatozoon drawn from an example which has passed into a collar-cell as in 

 fig. 9, S. The tail has been added from observation of ripening spermatids, and 

 this figure is thought to represent the ripe unchanged sperm of Gran/in compressa. 

 A.t AC is the acrosome. C'h.K. (See footnote on page 279.) 



