SPECIES HYBRID. iabrd 
There is no reason to suppose that the subfamily is not present in 
the other Pacific islands, but it has not been recorded from them.* 
With respect even to the Hawaiian Islands, Perkins (Fauna Haw., 1, 
elxxxix) says ‘‘Not less than 250 species [of Drosophilinz] must exist 
in the islands, and very probably double that number may occur.” 
The number and variety of Drosophiline form the most striking peculi- 
arity of the dipterous fauna of these islands. Nearly one-third of the 
species of Diptera considered by Perkins to be endemic in the islands 
belong to this subfamily. There are a number of large and strikingly 
colored species of true Drosophila, as I have convinced myself by an 
examination of material in the U. S. National Museum. Besides the 
two endemic genera mentioned above, there is a genus described by 
Grimshaw under the name Hypenomyia that is perhaps distinct, but 
is here tentatively placed as a synonym of Drosophila, in the absence 
of a satisfactory description. 
XIII. SPECIES HYBRID. 
Drosophila melanogaster and D. simulans are the only two species 
of Drosophiline that have been hybridized (see p. 14). The two 
species are extremely similar in appearance, and there is every reason 
for believing that they are closely related. This fact makes the 
hybrids less interesting for study than would be the offspring of two 
quite diverse species. In addition, the hybrids so far obtained have 
all been completely sterile, so that their genetic behavior can not be 
studied. Nevertheless, there are several facts of considerable interest 
in connection with the cross. 
In general, the hybrids are intermediate in appearance between the 
two parent species. This is true of the relative size of the eyes and 
width of the cheeks and of the male genitalia. The other differences 
between the species, except the length and shape of the egg-filaments, 
are too indefinite for exact study; and the hybrid females do not lay 
eggs, so that this character can not be observed. The hybrids differ 
from both parent species in several respects, as follows: 
1. They are completely sterile, and have poorly developed gonads. 
2. The abdominal plates often are irregular and have narrower and more irregular dark 
bands than are usual. 
3. Some of the thoracic bristles are usually missing. 
4, The wings are apt not to unfold properly, or to be somewhat less convex on the anterior 
margin than is usual. 
5. The cross-veins are often broken or missing. 
The most peculiar thing about these hybrids, however, is the distri- 
bution of the sexes. The crosses usually result as follows: 
D. melanogaster 2 X D. simulans & = hybrid @ 9 only. 
D. simulans 9 X D. melanogaster # = hybrid 3c; occasionally a few hybrid @ 9. 
If the D. melanogaster females bear a Y chromosome (X XY), and 
therefore give non-disjunctional exceptions, it is found that they 
* J had overlooked the fact that Jepson (1917, Ann. Rept. Div. Ent., Dept. Agric. Fiji, 1916, 
16) records Drosophila melanogaster from Fiji. 
