198 THOMAS H. BUYCE. 



Often one sees the chromatin collected to one side of this 

 plate ; sometimes the separate elements are widely scattered ; 

 in many instances, as in fig. 12, tliere are chain-like clusters, 

 Avhich suggest that a thread is being broken up into 

 segments, and in practically every ovum at this stage one 

 sees compound masses which are breaking down into the 

 separate elements which enter the equatorial plate of the 

 spindle. Hartmann, as already mentioned, has quite recently 

 described the chromosomes as arising directly from the 

 nucleolus. They arise as isolated rods, clumps, or threads 

 having the chromatin particles arranged in series in them. 

 The nature of my material makes it impossible for me either 

 to deny or affirm the direct origin of the chromosomes from 

 the nucleolus, but the appearances I have described are 

 not otherwise at variance with those described by Hart- 

 mann. 



I have between fifty and sixty sections of this stage, and 

 the relatively large number indicate that the prophase is 

 protracted. From the very first these always present the 

 same form. Fig. 14 shows a fragment of the thread com- 

 posed of spheres, united by a less deeply staining subtauce. 

 When separation is complete sixteen tetradal chromosomes 

 of nearly uniform appearance are found. When seen from 

 the side they have a dumb-bell shape, when seen en face 

 they are obviously the tetradal groups of authors. I have 

 counted the chromosomes at the various stages again and 

 again, and have always reached the number fifteen or sixteen. 

 Fifteen is an improbable number, and I feel sure that the 

 proper figure is sixteen. I have never succeeded in making 

 the number eighteen, which would be double the number 

 (nine) found by Boveri (1890) in Echinus microtubercu- 

 latus. R. llertwig (1896) made the number of chromosomes 

 emerging from the germ nucleus, in his experiments on the 

 development of unfertilised sea urchin eggs, sixteen or 

 eighteen, which would agree with my results. Field 

 (1893) in Fchinoderm spermatogenesis counted twenty-six to 

 thirty-two chromosomes in the spermatogonia, sixteen to 



