OF Till', (iKUM CELLS OF METAZOA. 



175 



individuals to determine this point, but, as has been already slated, in the four of the 

 thirteen testes which contained spermatogonia divisions exactly eleven chromosomes 

 were found to be always present. Obviously all of the eleven chromosomes cannot unite 

 into pairs during the synapsis, one must remain unmated, and this must be necessarily 

 that one of the first maturation division which does not appear bipartite. 



Now in those cases where there are eight chromatin elements present in the sperma- 

 tocytes the question becomes more complicated (Figs. 114-116). Here, as in the cases 

 where there are seven elements, one is central in position and distinguishable from the 

 others by its smaller volume, namely, the bivalent chromatin nucleolus (N. 2, Figs. 

 Ml lit'., in the last figure its univalent components separated); the remaining seven 

 elements are then chromosomes. As the lateral view, Fig. 1 1<;, of the spindle shows, four 

 of these are bivalent (the ones not marked by lettering). One (x) is oval in form, show- 

 ing no constriction or splitting, and so is probably comparable to the univalent chromo-. 

 some of those cells which contain but seven chromatin elements (i. c, to x in Fig. 113.) 

 There then remain the two elements marked a in Fig. 116, and each of these I conclude 

 must be a, univalent chromosome, which in cases where there are only seven chromatin 

 (dements in the spindle would have combined with the other to form one bivalent chromo- 

 some ; if this be so, then the transverse constriction of the left-hand chromosome marked 

 a in Fig. IK! would mil be the line of separation between two univalent chromosomes. 

 Another reason for looking upon these two chromosomes as univalent, is because they are 

 of approximately the same volume as the chromosome marked x, which we have shown 

 to be univalent by comparison with the chromosome x of Fig. 113. But there is a still 

 better reason for considering the (dements a of Fig. 1 L6 to be univalent chromosomes. 

 A pole view of a, corresponding stage with eight chromatin elements shows the seven 

 chromosomes frequently equidistant from one another (as in Fig. 115). But often we find 

 on pole view two of the seven chromosomes (dose together and connected by a band of 

 linin (a, Fig. 114); the two together constitute a virtual bivalent chromosome, which, 

 however, differs from the other bivalent ones in having its long axis parallel to the plane 

 of the equator of the spindle. Let the hand of linin which connects these chromosomes 

 <i become stretched out, and as a, result we would have a- bivalent chromosome lying 

 parallel to the plane of (he equator, and with its univalent halves widely separated — /'. e,, 

 the condition that maintains for the chromosomes a of Fig. 116. 



To summarize, we find two conditions in the spermatocytes: (1) there are seven 

 chromatin (dements, namely, one bivalent chromatin nucleolus, live bivalent chromo- 

 somes, and one univalent chromosome ; and (2) eight chromatin elements, namely, one 

 bivalent chromatin nucleolus, four bivalent chromosomes, one univalent chromosome 

 (corresponding to that of condition 1), and two other univalent chromosomes (which 



A. P. S. — VOI,. XX. W. 



