Baltzer has suggested on the basis of some observations that the larvæ while on the proboscis of the female absorb some substance secreted by the proboscis, and this substance accelerates the further development into a male and suppresses the female tendency. If this substance from the proboscis does not reach the larvæ the tendency to become males is gradually suppressed in the majority and only a few develop into pure males or protandric hermaphrodites, while the female characters are given a chance to develop. Baltzer assumes, therefore,--as it seems to us correctly--that in all larvæ the tendency for both sexual characters is present, that they are, in other words, hermaphrodites, but the chance for the suppression of one and the development of the other group of characters can be influenced by certain chemical substances which the larva may take up.[190] [190] Baltzer, F., _Mitteil. d. zoölog. Station_, Neapel, 1914, xxii. Giard has studied the effects of a curious form of castration brought about by parasites, which is followed by a change in the sexual character of the castrated animal. The phenomenon is very striking in certain forms of crabs when they are attacked by a parasitic crustacean, _Sacculina_. The two sexes differ in the crab _Carcinus mænas_ by the form of the abdomen, but when a male is attacked by the parasite its abdomen assumes the female shape. Smith observed in another crab that in such cases even the abdominal appendages of the male may be transformed into those of a female. The transformation is so complete that the older observers had reached the conclusion that the parasite attacked only the females, since they overlooked the fact that the castration by the parasite transformed the secondary sexual characters of the male into those of a female. Giard observed that in a diœcious plant, _Lychnis dioica_, a parasitic fungus brings about the transformation of the host into a hermaphrodite.