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 diplo-. 
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 spermatozo6n containing 
the monosome or large diplosome develops into a female, but when 
fertilized with a spermatozoén lacking the monosome or large diplo- 
some develops into a male. My own observations in Hippiscus 
indicate that a similar condition exists in the Orthoptera. It will be 
remembered that in the odgonia 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 explain 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 suecess. Paulmier 
(799) 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, 
