344 T. H. Morgan 
claws of the castrated male seem to be in most respects as like the 
juvenile claws as they are like those of the female. 
A number of infected crabs showed a condition of hermaphro- 
ditism, having, for example, the broad abdomen but with copu- 
latory styles on it. Smith concludes “that the male sex and prob- 
ably the male sex alone can be so radically modified in its sexual 
nature as to assume a perfect external hermaphroditism.” If, on 
the contrary, we assumed that we have here not hermaphroditism 
but an imperfect development of male characters combined with 
the juvenile condition, we might offer a plausible explanation of 
the facts. 
On the other hand two considerations of great weight point in the 
opposite direction. Smith found several cases in which the para- 
site had left the host and the latter had recovered. In such cases 
a perfect hermaphroditic gland regenerated that produced both 
spermatozoa and ova. One individual had developed both ovi- 
‘ducts and vasa deferentia. ‘This fact alone would demonstrate 
that the male crab is in reality heterozygous. 
Infected females never show the male characters, as is the case 
in castrated vertebrates, even when the ovary is completely re- 
moved. This might seem to show that in the crabs the female is 
homozygous, at least if the evidence for the vertebrates 1s logically 
applied to the crabs. There is, however a curious point here, 
seldom, if ever, noticed. Why should one expect, if both sexes 
have dual possibilities, that the destruction of the ovary causes the 
male characters to appear and the destruction of the testes the 
female? [see no logical grounds for such an expectation. 
THEORETICAL DISCUSSION 
In the unsettled condition of the evidence it is obvious that the 
problem of sex-determination has by no means reached a satisfac- 
tory solution. It is equally clear that a large amount of data is 
rapidly accumulating that promises to furnish an insight into the 
conditions that regulate sex. The evidence furnished by the 
phylloxerans shows that the parthenogenetic egg of the female has 
the dual capacity of producing either males or females. There 
