GAMKTOGENESIS AND FERTILISATION IN NEMATUS RIBESII. 105 



they show clearly about eight rather large chromosomes 

 in the equatorial plate, which split so that eight travel 

 towards each centrosome (fig*. 6 a, h). At a later stage the 

 testis becomes larger, and consists of lobes or compartments 

 in each of which all the cells are in about the same stage. 

 By the time the colours of the mature fly are beginning to 

 appear the testis contains nothing but spermatids and nearly 

 mature spermatozoa, but when the pupa is still white all 

 stages from spermatogonia to spermatids are found in dif- 

 ferent lobes, often ia the same section. 



In the nucleus before the first maturation divisions the 

 chromatin consists of a number of irregular masses (appa- 

 rently about eight, but they are always rather indistinct). 

 Shortly afterwards it becomes condensed into four more 

 concentrated masses, each of which frequently appears double 

 or quadruple (fig. 1 a,h, c). A spindle is then formed, and 

 the four chromatic masses become tightly packed together in 

 the equatorial plate, which is much smaller than in the 

 spermatogonial divisions. There are conspicuous centro- 

 somes. The chromosomes in the spindle are so tightly packed 

 together that it is difficult to be certain of their number, but 

 a comparison of many mitoses leaves little doubt that there 

 are four, each of which is bivalent (fig. 8 rt, h). The mitosis 

 appears to be of the heterotype form, resembling the figures 

 found by Moore in the cockroach ^ except that the chromo- 

 somes are fewer and very much smaller (fig. 9 a, h). They 

 are, however, appreciably larger than the chromosomes in the 

 maturation mitoses of the egg. 



The second maturation division is easily distinguished from 

 the first by the fact that the spindle is of about half the 

 diameter ; the chromosomes are usually even more tightly 

 packed, so as frequently to appear as a single body, but in 

 clearer cases there is little doubt that there are four (fig. 

 10 ft, h, c). At the telophase a vesicular spermatid nucleus 

 is formed, with the chromatin arranged round the edge 



1 ' Quart. Journ. Micr. Sci.,' vol. 48, 1905, pp. 489 aud 571. 



