THE ORIGIN OF GYNANDROMORPHS. 5 



single (haploid) nucleus would be male, all those from the double 

 (diploid) would be female. Moreover, if the two differ in one or more 

 characters, the male parts of the gynandromorph should be expected to 

 be like the mother, i. e., maternal, and the female parts should be 

 paternal if the paternal characters involved are dominant. The pos- 

 sibility of testing Boveri's hypothesis was pointed out by one of us 

 (Morgan) in 1905, and a test case was apparently furnished by a hybrid 

 gynandromorph of the silkworm moth described by Toyama. The 

 result was not in harmony with Boveri's hypothesis, but since the 

 relation of one or of two nuclei to sex was not then known for moths, 

 the case is not decisive, as will be shown more at length later. On the 

 other hand, Boveri's discovery of some preserved specimens of the 

 original Eugster gynandromorph bees and his analysis of their hybrid 

 characters seemed to show that the condition of these bees was com- 

 patible with his theory. This evidence will also be taken up more fully 

 later. We may anticipate our account of hybrid gynandromorphs of 

 Drosophila and state that they furnish direct evidence against Boveri's 

 hypothesis, for these flies at least. 



In 1905 Morgan suggested an alternative hypothesis based on the 

 fact that more than one spermatozoon had been found to enter the 

 bee's eggs. Should one only of these sperm-nuclei unite with the 

 egg-nucleus, the combination would give rise to the diploid cells of 

 the embryo, while if a second (or a third, etc.) sperm-nucleus should 

 develop it would give rise to haploid cells in the rest of the embryo 

 (fig. 1 B). On this view the haploid cells should be paternal and pro- 

 duce male parts, and the diploid cells maternal and produce female 

 parts, which is exactly the reverse relation in regard to parental 

 origin of the male and female parts from that expected on Boveri's 

 hypothesis. A decision as to which view is correct might be reached 

 in any special case in which sex-linked characters enter from the 

 paternal and maternal sides. As will be shown later, some of the 

 evidence from the Drosophila gynandromorphs is incompatible with 

 this hypothesis of Morgan. 



A third hypothesis that grew out of the work done in this labora- 

 tory was published in 1914 by Morgan, based on evidence from the 

 Drosophila cases. On this view the gynandromorphs are due to an 

 elimination of one of X chromosomes, usually at some early division of 

 the segmentation-nuclei. Rarely, in consequence of a delay in the divi- 

 sion of one of the X chromosomes, one of the daughter-halves fails to 

 reach its pole and is lost in the mid-plate or in the cell- wall (fig. 1 c). 

 As a result, the embryo comes to carry two kinds of nuclei, one kind 

 containing one X and the other kind two X chromosomes. The 

 critical evidence in favor of this interpretation is found in the presence 

 on both sides of the gynandromorph of other mutant characters whose 

 genes are not in the X chromosomes, but in autosomes. If, for example, 



