222 CHARLES W. METZ 



pairs of chromosomes. This will make clearer the exact points 

 at issue and facilitate subsequent discussion of the contrasting 

 views. The evidence which I wish to present may be considered 

 under three heads as follows: 



In the first place the number of chromosome pairs in diploid 

 groups is the same as the number of single chromosomes in ma- 

 ture germ-cells. Figures of the chromosomes in spermatocyte 

 divisions, either first or second, or both, accompany those of 

 diploid groups in most of the species included here, and speak 

 for themselves in this regard. A comparison of figures 13 and 

 15, 27 and 33, 24 and 25, 44 and 48, 52 and 53, 74 and 77, 125 

 and 126, 137 and 139, etc., clearly shows the relation between 

 haploid and diploid groups. In some species, the chromo- 

 somes are evident even in the spermatids leaving absolutely no 

 doubt as to the number contained in the spermatozoa. It must 

 be concluded, therefore, that fertilization results in a diploid 

 group in which the members of two haploid groups have associa- 

 ted in pairs, unless we resort to the very improbable assumption 

 that an eliminating process intervenes at some stage of fertiliza- 

 tion to throw out half of the chromosomes or to fuse them to- 

 gether two by two. Even this assumption, however, is over- 

 thrown by the relations of the sex chromosomes described below. 



Secondly, if the diploid metaphase group were not made up 

 of pairs, but were composed of double, univalent chromosomes, 

 the two elements of these double chromosomes ought to lie one 

 above the other, not side by side, in polar view, and in early 

 anaphase a haploid group should be seen going to either pole. 

 As a matter of fact neither of these conditions is realized outside 

 of the maturation divisions. The two members of a chromosome 

 pair lie side by side in metaphase, as shown by the figures, ex- 

 cept for an occasional displacement, and frequently all of the 

 chromosomes (the double number), may be seen dividing 

 (figs. 7, 8, 9, 16, 28, 32, 40, 77). The side by side association 

 and the method of division are clearly shown in figures 1-5, 7-9, 

 17, 19-24, 37, 39-46, 77, 98 and 99, etc. Figure 1, for instance, 

 is composed of five symmetrical pairs, the members of which 

 lie side by side. Figure 2 from the same species, shows similar 



