340 WILSON AND MATHEWS. [Vol. X. 



pigmentation, and size, there are some minor points of diver- 

 gence. 



The sperm enters the q%^ at any point of the periphery, and 

 an entrance cone, which soon disappears, is formed as it enters. 

 The middle-piece, which can be distinguished before entrance 

 (see Fig. 7, A), may still be seen in favorable cases immediately 

 after penetration (see Fig. 7, B). Shortly after entrance the 

 conical sperm-head rotates, but at times the aster develops at 

 the base of the head before rotation, showing conclusively 

 that it is derived from the base and not from the tip of the 

 sperm-head (see Fig. 7, D). This aster remains much smaller 

 than in Toxopneustes, and, in contrast to the latter, the sperm- 

 nucleus retains its conical shape, generally, until it has met the 

 egg-nucleus. No centrosome is to be found in the sperm-aster, 

 or in any subsequent stage of the development of the latter. 

 No radiations or centers are to be seen about the egg-nucleus 

 before the sperm reaches it. Preceded by its aster and blunt- 

 end first, the sperm advances to the egg-nucleus which puts out 

 a process to meet it (see Fig. 7, E and F). The two nuclei 

 meet in about five minutes ; the sperm-nucleus quickly becomes 

 vesicular, and later fuses completely with the egg-nucleus. 

 The small sperm-star, which has meanwhile been forced to one 

 side, now grows rapidly and gives rise to a large, granular, 

 archoplasmic-mass, difficult of analysis, which passes down 

 about the egg-nucleus (see Fig. 8, A). From the indefinite 

 periphery of this mass, coarse rays, staining blue in iron haem- 

 atoxylin and Congo red, run outward to the periphery of the 

 egg. Gradually this mass draws together at opposite poles of 

 the nucleus (see Fig. 8, B), the coarse rays disappear, and 

 there are formed two small, dense red-staining archoplasms, 

 surrounded by a blue halo of closely set, granular, fine astral 

 rays. These form the archoplasms of the first segmentation- 

 amphiaster (see Fig. 8, C). 



The central masses of these asters from now on stain a 

 bright vermilion in the double stain. They do not greatly in- 

 crease in size, although the nucleus increases in bulk over 

 eight times (see Fig. 8, C), until the separation of the chromo- 

 somes, when they grow rapidly and reach their maximum as 



