Other cases amongst the Anura have been recorded by Loisel and by Marshall, Spengel, and Knappe. In the early stages of the gonad in frogs there appears to be an hermaphroditic stage in which egg mother-cells and sperm mother-cells are both present, at least in those individuals that will later become males (Kusakowitsch). The normal hermaphroditism of certain fish (_Serranus_) and its rare occurrence in other species (recorded by Shattuck and Seligmann) need not be recorded here.[18] D. EVIDENCE FROM CRUSTACEANS. In the Crustacea the secondary sexual characters are not marked, except in a few cases. In the amphipods, Holmes has shown direct contact plays the chief rôle in mating, and in the crayfish it has been shown by Dearborn, Andrews, and Pearse that sex recognition is largely tactile. Chidester also has shown this in crayfish. Even in crabs, and especially those living on land which have well-developed eyes and good vision, secondary sexual differences are as a rule slight and the mating instincts simple. On the other hand, the enormous chela of the male of the fiddler is supposed to be a secondary sexual difference (mainly because no other use for it has been found). Pearse suggests that the waving of this claw by the male is used as a sex signal, although he is disinclined to accept Alcock’s view that it has become “conspicuous and beautiful in order to attract the female.” The most remarkable case known of a change in the secondary sexual characters of one sex into those of the other was discovered by Giard in 1886. As a result of infection by parasitic crustacea (_e. g._, _Sacculina_), the male crab develops the secondary sexual characters of the female. It has been generally supposed, following Giard, that this result is due to the destruction of the testes of the male by the roots of the parasite that invades the spaces between the organs of the host, and, in the case of the testis, ultimately brings about its partial or complete destruction. Not unnaturally the results here were supposed to be parallel to those of castration in vertebrates, and received in fact the name of “parasitic castration.” More recently Geoffrey Smith has studied this phenomenon in the crab _Inachus_, infected by the parasite _Sacculina_, and has reached the conclusion that the change is not due to injury or to destruction of the testes, but to a change in the metabolism of the crab brought about by the parasite.