THE ORIGIN OF GYNANDROMORPHS. 13 



There are, however, other theoretical possibilities that should be 

 noticed, for it is possible that gynandromorphs may sometimes arise 

 in other ways. In fact, one or two of those we describe may be ex- 

 plained in the following way : An X egg fertilized by a Y sperm (a regular 

 male), might later become partly female, i. e., gynandromorph, through 

 somatic non-disjunction, both daughter X's remaining in the same cell 

 at some early embryonic division. Parts descended from the XX Y 

 cell are female; the other (Y) cell would presumably die. If such a 

 process occurred at the first division and all of the yt>lk was later occu- 

 pied by the viable XXY cells, the embryo would become entirely 

 female, although containing only sex-linked genes from the mother, 

 and might be mistaken for a case of 'primary non-disjunction.' 



A non-disjunctionally produced egg containing a Y chromosome 

 or an egg without a sex chromosome fertilized by an X sperm might 

 also, starting as a male, produce a purely paternal female or female 

 parts (mosaic) through somatic non-disjunction. If non-disjunction 

 occurred at a late division a proportionately smaller part of female 

 tissue would be formed and the regular male cells formed earlier would 

 give male parts i. e., the individual might be more male than female. 



There are no cases where these explanations only will apply, but a 

 few cases accounted for by chromosome elimination may be also 

 explained in one or the other of these ways, viz, that the gynandro- 

 morph started as a male. 



CYTOLOGICAL EVIDENCE OF CHROMOSOMAL ELIMINATION. 



The most important case of chromosomal elimination involving 

 one of the sex chromosomes, and therefore most like the case of 

 gynandromorphism in Drosophila, has been described in Ascaris 

 (Rhabditis) nigrovenosus by Boveri and by Schleip. In this nematode 

 there is a hermaphroditic generation that lives in the lungs of the 

 frog. Eggs and sperm are produced at the same time in the her- 

 maphroditic gonad. The full number of chromosomes is the same 

 in the early oogonia and spermatogonia. This number is reduced to 

 half in the egg and also in the sperm at the reduction division, but 

 while all the eggs are alike, there are two kinds of spermatozoa, one 

 containing one less chromosome than the other. This loss of one 

 of the chromosomes in one-half of the sperm-cells is apparently brought 

 about as a regular process by the failure at reduction of one member of 

 the paired sex chromosomes to reach the pole. It is caught at the 

 division plane or else remains near that plane and disappears. This 

 process differs however, from what we suppose to occur in eliminating 

 a sex chromosome in Drosophila when a gynandromorph is produced 

 in that an undivided X is lost. Whether in Ascaris this process occurs 

 in all the cells at a given division or is somewhat irregular is not certain, 

 and can only be determined by a fuller knowledge of the ratio of males 



