2l8 MARY T. HARMAN. 



they have divided at the point of union as we have previously 

 seen. As the result of this division the chromosomes of the 

 anaphase are ovoid. The X-chromosome does not divide in this 

 division but passes to one pole much in advance of the others. 

 The first division then is truly a reductional division. 



The spindle of the secondary spermatocyte is nearly spherical. 

 Early in the metaphase the chromosomes show a longitudinal 

 split (Figs. 28 and 29). All of the chromosomes divide in this 

 division. It is an equational division in the sense of the dividing 

 of the chromatin material of original chromosomes into halves. 



4. The X-Chromosome. 



The X-chromosome is a persistent portion of chromatin ma- 

 terial which can easily be identified throughout the growth period. 

 It never becomes finely granular, nor does it have the woolly 

 appearance of the other chromatin elements. The other chromo- 

 somes lose their identity in the coiled thread, but the X-chromo- 

 some does not form a part of this coiled knot. With the formation 

 of the primary spermatocyte chromosomes it may be distin- 

 guished from the others both by its shape and by its more compact 

 appearance. On the primary spermatocyte spindle it is often 

 found half way to the pole before the other chromosomes have 

 completely divided. It is more difficult to recognize it in the 

 secondary spermatocyte because all the chromosomes here are 

 ovoid in shape, and the differences in size between some of the 

 chromospmes are so much less. It behaves similarly to the 

 other chromosomes here, neither being precocious in its division 



nor lagging. 



DISCUSSION. 



Concerning many of the most obvious and essential points of 

 the behavior of the chromatin in the maturation of the sperm, 

 there is no longer any debate. It is agreed that during this 

 period the number of chromosomes is reduced to one half. That 

 this reduction in number is brought about by the union of chro- 

 mosomes by pairs is also generally accepted. As to how this 

 pairing has taken place has been the subject of much discussion, 

 and upon the answer to this question depends the acceptance or 

 rejection of other theories. It seems to the writer that when we 



