WENRICH: spermatogenesis of PHRYNOTETTIX MAGNUS. Ill 



Miss Nowlin ('08) describes for Melanoplus bivittatus a precocious 

 tetrad (no. 11), which always appears in the metaphase as a rod 

 extended parallel to the spindle-axis. Such is also the behavior and 

 form of chromosome A. Furthermore, I have examined slides of 

 Melanoplus material and find that it also has a spireme loop that stains 

 more deeply than the others. May not this precocious tetrad of 

 Melanoplus be related to chromosome A of Phrynotettix? 



Early in the course of my investigation I had the opportunity of 

 looking over some of Dr. McClung's collection of slides of acridian 

 material, and, though a thorough study was not made, I could easily 

 recognize in the pachytene stage of a number of species a spireme loop 

 which stained more deeply than the others. Such loops were found, 

 for example, in species of Aeoloplus, Amphitornis, Arphia, Brachy- 

 stola, Hadrotettix, Hesperotettix, Hippiscus, Melanoplus, Phaetaliotes, 

 and Stenobothrus. One characteristic of such tlireads, which, how- 

 ever, is not so marked in Phrynotettix, is a tendency to become asso- 

 ciated with the accessory chromosome. This is particularly true of 

 Melanoplus and Stenobothrus, the forms in which Davis ('08) was led 

 by this close association to describe a "double monosome." There 

 can be no question, I think, that these "double monosomes" were 

 merely the accessory chromosome plus one of these deeply stained 

 spireme segments. In view of these facts, the suggestion offers itself, 

 that similarity in the properties and behavior of certain chromosomes 

 in different species may be correlated with their taxonomic relation- 

 ships. Such correlation was, indeed, seen and discussed some time 

 ago by McClung ('08a). Meek ('12) has already made a comparative 

 study of the sizes of the chromosomes in several species of Steno- 

 bothrus, and has reached the conclusion that the five smaller pairs 

 of chromosomes are of the same size in all species, but that the large 

 (V-shaped) pairs differ from one species to another. It still remains 

 to be seen whether or not the chromosomes of different species can be 

 compared on the basis of their details of organization and behavior, 

 as well as size. 



2. The heterochromosomes. — I believe most observers agree that 

 the heterochromosomes maintain their individuality tlii'ough the 

 growth-stages of the male germ-cell cycle. On another page (p. 87) 

 I have called attention to the similarity in behavior between the 

 autosomes and the accessory, this has also been noted by many others, 

 so that there is no very good ground for setting up a claim to funda- 

 mental distinction between the two kinds. It seems to me, therefore, 

 that if we admit a persistent individuality for the heterochromosomes. 



