136 bulletin: museum of comparative zoology. 



Various combinations of the allosomes in the same species occur 

 in the Hemiptera, where they have been described by Wilson and 

 Montgomery. 



A glance at the above classification will show that among insects 

 the first type of monosome (A 1) is characteristic of the Orthoptera, 

 although it occurs in a few instances in the Hemiptera and Coleoptera. 

 In the Orthoptera it has been found in all the forms investigated with 

 the exception of Syrbula, Stenopelmatus, and Periplaneta. In Syrbula, 

 one of the Acrididae, Montgomery (:05) found that the allosome of 

 the spermatocytes is represented in the spermatogonia by two elements 

 of equal size and is therefore a diplosome. During the early growth 

 period the di})losomes become joined end to end to form a rod shaped 

 element, which retains its compact structure and during the prophase 

 of the first division becomes bent into a V. It divides reductionally 

 in the first division and equationally in the second. These results of 

 Montgomery's need confirmation, since all other observers who have 

 traced the history of the allosome in the Orthoi)tera have found that 

 it is unpaired in the spermatogonia and does not divide during the 

 first division. Montgomery's Figure 33 is suggestive of an interpreta- 

 tion different from his, in that it shows a chromosome attached by 

 mantle fibers to only one spindle pole, a condition that I have found to 

 be realized in all the forms I have studied. INIontgomery, however, 

 believed that later this element divides. To quote : — "In a number of 

 cases after nine of the chromosomes were arranged in the equator and 

 some of these were beginning to divide (Fig. 33) one (y) had not yet 

 taken up that position but lay nearer one spindle pole than the other. 

 This was the case e. g. with four cells in exactly the same stage lying 

 in the same section of one testicular follicle, and in all of these the 

 isolated chromosome was of the same size and form, straight, and 

 appearing to consist of two closely apposed arms. It may be that this 

 is the heterochromosome, with which it agrees in general form and size, 

 but this could not be definitely determined; ultimately it takes a 

 position in the equator and divides with the others." 



In Stenopelmatus Miss Stevens (:05'^) has found that a conspicuous 

 element, colored deeply with chromatin stains, appears in the early 

 spermatocyte but is not represented in the spermatogonia. This 

 peculiar element "first appears attached to an end of the spireme in 

 the growth stage of the young spermatocytes, where it is much smaller 

 than in later growth stages. It gradually increases in size, is a con- 

 spicuous element in the first maturation spindle, goes into one of each 

 pair of spermatocytes of the second order, and then degenerates during 



