WILCOX: SPERMATOGENESIS. 13 



The number relationships of the chromosomes in the spermatogenesis 

 of Caloptenus may be thus tabulated : — 



Spermatogonia 12 univalent chromosomes. 



Spermatocytes, 1st order 6 quadrivalent chromosomes. 



Spermatocytes, 2d order 6 bivalent chromosome.-. 



Spermatids 6 univalent chromosomes. 



Expressed in individual chromosomes: — 



Spermatogonia 12 Spermatocytes, 2d order . 12 



Spermatocytes, 1st order . 24 Spermatids 6 



Spermatids immediately after the second spermatocyte division are 

 shown in Plate III. Figs. 125, 129, and Plate V. Fig. 232. There is at 

 first no nuclear vacuole surrounding the six small spherical chromo- 

 somes, which are closely packed together, and immediately surrounded 

 by the granular cytoplasm (Plate III. Figs. 125, 126, 129). The in- 

 terzonal filaments are still to be seen, forming a striated body, probably 

 the beginning of the " Nebenkern," as suggested by Platner ('8G). 



Some of the spermatids stained by Henneguy's method, and nearly 

 all of those stained by Heideuhain's method, show a spherical body near 

 the chromatic mass (Plate V. Figs. 232—235), and this body becomes 

 included in the nuclear vesicle when a membrane is formed (Plate IV. 

 Figs. 140, 141, Plate V. Figs. 232, 236). I regard this body as the 

 centrosome which is left in each spermatid after the last spermatocyte 

 division, and I also believe it to be identical with the very conspicuous 

 body which forms the neck of the spermatozoon (Plate V. Figs. 196-200). 

 The chromatic substance fuses into a smoothly contoured mass, which 

 soon assumes the crescent shape so common in insect spermatogen- 

 esis. The neck-body lies within the nuclear membrane opposite the 

 concavity of the chromatic crescent (Figs. 198-200). The chromatin 

 undergoes chemical and physical changes during the metamorphosis of 

 the spermatid, but the neck-body remains practically the same in size, 

 and does not alter its affinity for stains. It becomes the neck of the 

 spermatozoon (Plate IV. Figs. 139-158, Plate V. Figs. 196-200). The 

 chromatic crescent is at first less dense, and stains less deeply ; then it 

 becomes concentrated, and stains nearly black by Heideuhain's method. 

 These changes in density are not well shown in the figures. At the 

 same time it becomes elongated, one end applying itself to the neck- 

 body, the other becoming the tip of the spermatozoon head. 



The nuclear vacuolation, much reduced, persists for some time near 

 the neck-body (Fig. 196), then disappears entirely, and the further 



