138 bulletin: museum of comparative zoology. 



Among the most interesting phenomena exhibited by the monosome 

 in the Orthoptera are the different forms which it assumes during the 

 growth period, de Sinety (:01) first showed that in the Phasmidae 

 the monosome becomes much elongated during this period and in 

 some cases may be in direct connection with the spireme, while 

 McClung (:02) and Otte (:06) have shown that in the Locustidae the 

 monosome becomes converted into a long coiled thread. According 

 to Otte this thread shortens and thickens to form a loop, which by the 

 apposition of its arms becomes converted into a longitudinally double 

 rod. My own observations have shown that in the Acrididae the 

 monosome has a somewhat similar history, although there is con- 

 siderable variation in the different subfamilies. In Steiroxys, how- 

 ever, the monosome apparently remains more compact than in most 

 of the Locustidae. The entire history of this element is strikingly 

 like that of the autosomes, but with this difference : — in the monosome 

 the different autosome stages have been suppressed to a very large 

 extent. It is only necessary to add that it forms a modified spireme 

 and is attached to the distal pole in the same manner as the auto- 

 somes, although in the monosome the spireme is found at a consider- 

 ably later period. 



In the Orthoptera, as in other insects, the monosome often shows 

 a distinct bipartite structure. This is especially true of Stenobothrus 

 and Melanoplus, where, as I have shown, during a large part of the 

 growth period the monosome is composed of two distinct and dis- 

 similar portions. 



McClung (:05) has described some peculiar relations between the 

 autosomes and monosome in certain Orthoptera. In several species 

 the monosome becomes attached to a bivalent (in Mermiria quad- 

 rivalent) autosome during the prophase of the first division and this 

 association persists throughout the maturation period. A similar 

 condition was noticed by de Sinety in the phasmid Leptynia. I have 

 been unable to find anything of the kind in any of the Orthoptera 

 studied. However, a comparison of McClung's figures with some of 

 the stages of the monosome in Stenobothrus suggest that possibly in 

 some cases he has mistaken the more granular component of the 

 monosome for an autosome. 



Regarding the relation of the monosome of the Orthoptera to the 

 allosomes of other arthro])ods, it is probably directly comparable with 

 the monosomes of other forms, whether they divide in the first or 

 second division, since the time of division would seem to be a character 

 of secondary importance. In regard to its connection with the diplo- 



