DAVIS: SPERMATOGENESIS. 139 



somes, we are apparently on less certain ground. Wilson has sug- 

 gested that the monosomes simply result from a further modification 

 of the unsymmetrically paired diplosomes, the smaller component 

 of the pair having been lost altogether. On this view it seems impos- 

 sible to account for their frequent bipartite structure, which has led 

 Montgomery (:05) to argue that the monosome may be formed by 

 the permanent fusion of a diplosome pair. However, he later (:06) 

 pointed out that there are difficulties in the way of such a view, since 

 Stevens (:05, :06'') and Wilson (:05 to :06) have shown that where 

 there is a monosome in the male there is a symmetrical pair of chromo- 

 somes in the female, and where in the male there is a pair of tliplo- 

 somes of unequal volume these are represented in the female by a pair 

 of equal volume. This of course means that in species where the 

 spermatozoa are dimorphic, one-half containing a monosome and the 

 other half lacking this element, the mature eggs are not dimorphic, 

 for each contains the equivalent of a monosome. Similarly, in cases 

 where one-half the spermatozoa contain the large, the other half the 

 small diplosome, all the mature eggs contain a chromosome corre- 

 sponding to the large diplosome. From this both Stevens and Wilson 

 conclude that an egg when fertilized with a spermatozoon containing 

 the monosome or large diplosome develops into a female, but when 

 fertilized with a spermatozoon lacking the monosome or large diplo- 

 some develops into a male. jNIv own observations in Hippiscus 

 indicate that a similar condition exists in the Orthoptera. It will be 

 remembered that in the oogonia of this species there is a symmetrical 

 pair of chromosomes which correspond to the monosome in the 

 spermatogonia. This being the case, it is difficult to ex])lain the 

 monosome as originating by the permanent fusion of two formerly 

 distinct elements, for on this view it would seem that the number of 

 chromosomes in the female should be one less than in the male, instead 

 of one more as is actually the case. Unfortunately we know nothing 

 concerning the behavior of the allosomes or their equivalents during 

 the maturation and fertilization of the egg and until these stages have 

 been fully elucidated we can scarcely hope to arrive at any adequate 

 explanation of their origin. 



A number of theories have been developed regarding the function 

 of the allosomes, but so far with very indifferent success. Paulmier 

 ('99) and Montgomery (:01) have suggested that they are degenerating 

 chromosomes, but ^Montgomery has recently (:06) receded from his 

 former position, holding simply that their function must be very dif- 

 ferent from that of the autosomes, as indicated by their structure. 



