240 CHARLES W. METZ 



exhibited by this and other species of Bombyhidae. Figures 

 129 to 133 are only a few from among scores of similar ones 

 studied. In all cases the five large pairs and often the small 

 pair stand out clearly and show a close approximation. The 

 figures need little explanation beyond that given already for 

 preceding species. Numbers 129 to 131 are spermatogonial 

 prophases showing the five long and one short double threads, 

 which later loosen up and contract to form the metaphase pairs 

 shown in figures 132, 133. 



Anthrax sinuosa (figs. 134-140). This species is very inter- 

 esting from several standpoints. In the first place it possesses 

 chromosome pairs of various sizes (figs. 134-137), which clearly 

 illustrate the pairing of corresponding chromosomes. Secondly 

 the evident dissimilarity between A. sinuosa and A. lateralis 

 in number of chromosomes, the former having 18, the largest 

 group in any fly within my knowledge, and the latter possess- 

 ing but twelve, presents the greatest divergence of this nature 

 that I have observed between two species in one genus. Thirdly, 

 the sex-chromosome pair is apparently one of the largest in 

 the group, instead of the smallest, as has been the case in all 

 of the above species exhibiting a conspicuous inequality between 

 X and Y. Unfortunately I have been unable to identify the 

 sex-chromosome pair in A. lateralis. If the small pair in A. 

 lateralis (figs. 132, 133) is the sex-chromosome pair, as it "is in 

 many flies, then a remarkable difference exists between the 

 sex-chromosomes of the two species, such a difference as I have 

 found in no other closely related flies. Similar differences have 

 been observed between related species of Hemiptera and Coleop- 

 tera, but seem to occur very rarely among the Diptera. In 

 maturation divisions of this species (figs. 138-140) the short 

 chromosomes show a tendency to become rounded, but the rela- 

 tive sizes are readily seen to correspond with those of the dip- 

 loid groups. Figures 139 and 140 (second spermatocytes) 

 appear to be respectively X- and Y- containing groups. As 

 the spermatogonial figures (134-137) show, X is the largest 

 chromosome present, while Y is smaller than the two largest 

 autosome sizes. Comparing figures 139 and 140 it may be seen 



