6. Special Reference of the phenomena of Parasitic Castration to High and Low Dimorphism. ()| 



here that an essentially similar process, namely the passage of particular males from sexual 

 activity with well developed secondary sexual characters to a condition of sexual suppression 

 has been previously observed by Faxon in Cambarus (Ann. Mag. N. H. (5) Voi. 13 1884), an 

 observation which escaped my notice.) 



It appears to me certain that the two phenomena of definitive and facultative dimor- 

 phism are essentially due to the same cause, namely to the antagonism that exists between 

 the functional activity of the sexual organs and growth of the body as a whole in the male 

 sex. It must be borne in mind that this antagonism appears to result in the phenomena of 

 high and low dimorphism only in the male sex. An explanation of this peculiar relation 

 in the male sex between sexual activity and growth is, I think, obtained by a consideration 

 of the results arrived at from our study of the phenomena of Parasitic Castration, and also 

 from certain other facts which I will introduce later. 



In Parasitic Castration we have found that the male reacts to the presence of the 

 parasite by producing in its body an hermaphroditic substance as opposed to a male sub- 

 stance, and as a result of this the testes become greatly reduced or even disappear and the 

 secondary sexual characters talee on a female character. The reason for this behaviour is, 

 I think, to be found in the adaptive regulation of the metabolism so brought about, in order 

 that the animai may withstand better the attack of its parasite. This adaptive regulation 

 consists in the production of at least a partially female condition of metabolism as opposed 

 to a wholly male condition, the female condition being (to use the terminology of Geddes 

 and Thompson, Evolution of Sex. in: Internat. Se. Series) preponderantly anabolic or conser- 

 vative, as opposed to the katabolic male condition, and by this change from a katabolic to a 

 more anabolic condition the animai can withstand better the drain on its system occasioned 

 by the parasite. Now in the phenomenon of high and low dimorphism an exactly parallel 

 state of things occurs. The male in order to grow must suppress the male condition of its 

 metabolism and cali into activity the female or anabolic condition or substance, which from 

 the facts of Parasitic Castration we believe every male to possess in a latent state. The result 

 of this is that we get the suppressed sexual condition (really a semi-hermaphrodite con- 

 dition) in the middle-males of species, such as I. scorpio, which exhibit facultative high and 

 low dimorphism, while in species with definitive high and low dimorphism we get the condition 

 of sexual suppression i. e. semi-hermaphroditism relegated to a purely larvai state, i. e. in 

 certain individuals, perhaps partly owing to external conditions of nutrition, sexual maturity 

 is put oif (high males), while in others it is hastened on (low males). 



I have recently come upon a most convincing piece of evidence to show that in the 

 condition of sexual suppression, characteristic of high and low dimorphism, we are really 

 dealing with a semi-hermaphrodite state exactly parallel to the condition called forth in in- 

 fected males by Parasitic Castration. This evidence is derived by a reexamination which 

 I have made this year of the sexual condition in Orchestici deshayesii and gammarellus , the 

 common Sand Hoppers. 



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