242 CHARLES W. METZ 



very nearly the same size, but even they may be distinguished 

 in some figures (note especially figures 143 and 144). 



Asilus lecythus (figs. 146-148). Scarcely less striking in the 

 matter of size differences is the evidence presented by this 

 species. Upon close examination its seven pairs (or its seven 

 single chromosomes in haploid groups) are seen to be definitely 

 graduated in size from the smallest to the largest. The grada- 

 tions are somewhat confused in the diploid groups by the uneven- 

 ness and the flexures of some of the chromosomes, but in hap- 

 loid groups (fig. 148, second division) the gradation is much 

 more conspicuous. The sex-chromosomes, apparently, are not 

 unequal. 



Asilus notatus (figs. 149, 150). What has been said of the 

 last species (A. lecythus) applies equally to the present one, 

 except that the size differences between the larger pairs are 

 scarcely distinguishable. Figures 149, 150 show spermatogonial 

 and second spermatocyte groups of this species. 



Leptogaster hadius (figs. 151, 152). The diploid group of 

 this species is shown in figure 151. As may be seen it consists 

 of five pairs, only two of which may be differentiated by size. 

 The largest of these is the sex-chromosome pair, whose mem- 

 bers, as in previous cases are frequently not associated during 

 metaphase. The haploid group is indicated by figure 152 

 (second division). 



Erax rufibarhis (figs. 153, 154). In this species, also, five 

 rather similar pairs of chromosomes are found. As in the pre- 

 vious case only the smallest and largest (sex chromosome pair) 

 may be differentiated. Figure 153 shows the chromosomes in a 

 flat plate and indicates their size relations. In spermatocyte 

 divisions the chromosomes of E. rufibarbis show a decided ten- 

 dency to condense and become rounded, but the size relations 

 are nevertheless conspicuous (fig. 154). This tendency toward 

 condensation extends even into the spermatids, thus enabling 

 one to count the chromosomes with ease, and to determine with- 

 out doubt the number of chromosomes carried by the spermato- 

 zoan into the egg. 



