96 THE ORIGIN OF GYNANDROMORPHS. 



Giard, and later Geoffrey Smith, have described the changes that 

 take place when crabs are parasitized by Sacculina and other para- 

 sitic Crustacea. When the male spider-crab Inachus dorsettensis is 

 parasitized by Sacculina the abdomen becomes wide like that of the 

 female, and its posterior appendages, that are absent in the male, 

 develop and become somewhat like those of the female. The chelae 

 likewise come to resemble those of the female. The testis, which 

 may not be affected at first, may later degenerate to some extent, and 

 in one case after the parasite had fallen off the regenerating testis 

 produced eggs. It was formerly supposed that the degeneration of 

 the testis might be the cause of the change in the secondary sexual 

 organs, although no such relation between gonad and soma is known 

 to exist in this group; but the work of Geoffrey Smith seemed to him 

 to suggest that the results are directly caused by the parasite itself 

 by stimulating the formation of fatty substance whose presence in the 

 blood may cause eggs to develop and the secondary sexual organs of 

 the female to appear. In other words, "the crab comes to resemble 

 a female because the physiology of its body-tissues has been changed 

 from the male to the female type" (Doncaster). Whatever the 

 explanation may ultimately be found to be, the fact of the change is 

 important. The result falls into line with the other evidence con- 

 cerning sex determination in the Crustacea, viz, that maleness and 

 femaleness are not so fixed by internal genetic factors if such exist, 

 but that the balance may be shifted by other agents as well. A parallel 

 case is known in the Andrenine bees, parasitized by another insect, 

 Stylops. According to Perez, the stylopized males come to resemble 

 in certain respects the females, and inversely the stylopized females the 

 males. The sex-glands are not always affected. If in bees as in 

 moths the secondary sexual characters are independent of the gonads, 

 the effect of Stylops must be either directly on the host or through a 

 change in its metabolism. W. M. Wheeler has described stylopized 

 American wasps of the genus Polistes. No change hi the secondary 

 characters takes place, at least not to any marked extent. 



The decapods have, as a rule, males and females sharply dis- 

 tinguished, although the females of Gebia major have only ovaries, the 

 males have, behind the testes, ovaries more or less developed. A 

 crab, Lysmata seticaudata, has as a rule both ovaries and testes, with 

 their ducts. Several hermaphroditic crayfish have been described, 

 especially by Faxon (1898) and Hay (1907). One (text-figure 69) had 

 ovaries on both sides, also on the right side a testis (without sperm) 

 and a vas deferens. It had the external characters of a "first form" 

 male except for the openings of the oviducts on the third pair of legs. 

 It appears, at least in the genus Cambarus, that hermaphroditic indi- 

 viduals are females which, "owing to some ambiguity of the formative 

 cells in the embryo, have developed to a greater or less degree the 



