508 



larger and one of the small ones considerably smaller than the other. 

 However, there is some slight fluctuation in the relative sizes although 

 the proportions as indicated usually hold true. The small one is as a 

 rule not quite so small as the small one seen in the preceding divi- 

 sion. This is doubtless accounted for by the fact that in pairing in 

 the secondary spermatocyte it would have no mate of its own size 

 but would have to unite with one of larger size. 



Figs. 23 and 24 are camera lucida drawings of secondary sperma- 

 tocytes which contain four chromosomes in the prophase of division. 

 Fig. 23 is from a section and Fig. 24 from a smear preparation. 

 Figs. 26, 27, 28 and 29 show the chromosomes in anaphase. Fig. 25 

 is a side view of the spindle bearing four chromosomes, drawn from 

 a smear preparation. What has just been stated regarding the size 

 and appearance of the four ordinary chromosomes in spermatocytes 

 which bear the odd chromosome is true likewise of the four chromo- 

 somes of the spermatocytes devoid of it. 



As to the exact nature of the divisions of the chromosomes in 

 the respective spermatocytes little could be determined. In the primary 

 spermatocyte the odd chromosome does not divide and the others which 

 are all presumably bivalent become constricted at their mid-points in 

 the same plane as that of the general equatorial plate and ultimately 

 move apart to the poles of the spindle. Their compact form and their 

 more or less spherical or oval shape prevents one from drawing any 

 direct conclusion as to whether or not the divisions are qualitative. 

 It may be pointed out, however, that the division differs in appearance 

 from that of the secondary spermatocyte where the chromosomes fre- 

 quently become drawn out into an elongated body which then ap- 

 parently splits lengthwise as shown in Fig. 30 which represents two 

 adjoining chromosomes of a secondary spermatocyte in process of 

 division. It was not unusual in this second division to find some two 

 or three chromosomes lagging, as it were, and dividing in this way, 

 the other chromosomes having already divided and migrated to the 

 poles. However, even here one cannot be absolutely certain of the 

 nature of the division because the shape of the individual chromo- 

 somes in prophase is such that it is impossible to determine the rela- 

 tive positions of the component chromosomes which have paired to 

 form the larger ones that ultimately divide. 



As already noted the odd chromosome almost invariably lags at 

 the last division and, furthermore, in many instances it may be seen 

 to be dividing longitudinally. 



The meaning of the second conjugation remains an enigma. Thai 



