THE ORIGIN OF GYNANDROMORPHS. 95 



been reported, according to Hull, and one or two other gynandromorphs 

 incompletely described. 



Most of the gynandromorphs in spiders belong to one family. Thus 

 amongst the 232 species of British Linyphiidse there are seven gynan- 

 dromorphs known, while amongst the 377 other species only one. 

 Hull estimates that gynandromorphs are nine times as frequent in 

 the Linyphiidse as in all the rest taken together. 



Since the male is heterozygous for the X chromosome in spiders the 

 results may have the same explanation as in insects, but since no 

 hybrid-gynandromorphs have been found it is impossible to do more 

 than point out a possible solution. 



GYNANDROMORPHS IN CRUSTACEA. 



The frequency of bilateral gynandromorphs in insects is in marked 

 contrast to the almost total absence of such types in the large group 

 of Crustacea. It is true that in the latter there are examples of inter- 

 sexual individuals, but it is not clear whether these come under the 

 same category as the gynandromorph insects or are special cases more 

 like hermaphrodites. 



It may be of interest to observe in this connection that in the 

 Crustacea no sex chromosomes have as yet been discovered, but it 

 may be replied that this may be due to the well-known difficulties of 

 technique rather than to a real difference. However this may be, 

 there are certain well-ascertained facts about some of the Crustacea 

 suggesting that the condition of hermaphroditism is, so to speak, nearer 

 the surface in the sense that the swing towards one sex or the other in 

 a given individual is brought about more readily by age or environ- 

 mental conditions than in other groups where a change is more difficult 

 because the internal hereditary factor differences prevail over ordinary 

 external or age differences. For example, in the group of cirripeds 

 hermaphroditic species and species with separate sexes exist, as well 

 as species related to hermaphroditic species in which the females have 

 complemental males. It has been suggested that these males are 

 themselves only those arrested females or hermaphrodites that settle 

 down and become parasitic on the larger sessile females; in other words, 

 that these males had the potentiality of becoming females if they had 

 chanced to lead a different existence. There are families amongst 

 the isopods that are hermaphroditic. Certain species of amphipods 

 are said to be males when young, females when older. Eggs have 

 been found at certain stages intermediate in size between the small 

 male-producing eggs and larger female-producing eggs. 



The transformation of some of the secondary sexual characters of 

 the male into those of the female in certain parasitized crabs has a 

 bearing both on the relation of these characters to the sex-glands and 

 possibly also on the causes that determine sex in the Crustacea. 



