Q n The effect of the Parasites on their hosts. 



Nebeski (Amphipoda Adriatica. in: Arb. Z. Inst. Wien 3. Bd. p. 134) originally found 

 tbat in a large proportion of tbe males of Orchestia gammarellus immature ova are present in 

 the anterior region of the testes, which however never come to maturity. 



Dei.i.a Vaixe Gammarini. in: Fauna Flora Golf. Neapel 20. Monogr. 1893) in trying 

 to confirm Nebeski's observations throws some doubt on their validity, as he remarks that he 

 has never found the ova in fully developed males but only in occasional males which have 

 failed to develope complete male characters. 



The discrepancy between these two results is so striking that I determined to look 

 into the matter, and the solution of the difficulty, though not yet complete, has been of some 

 interest. In the bays of Naples and of Pozzuoli both O. deshayesii and O. gammarelbts are 

 very common, but during the winter months they lie hidden under stones and refuse and require 

 some looking for. During the months December-March I have collected very numerous spe- 

 cimens of O. deshayesii, and on dissecting them I found that more than half the males, 

 whether fully developed or not and of all sizes, exhibited the ova in their testes. 

 It is clear therefore that Della Valle cannot have examined O. deshayesii at Naples during 

 the winter months, and that during the summer months, when O. deshayesii breeds, 

 the fully developed males lose these ova 1 . 



Now in confirmation of this, I have found that O. gammarellus at certain places, e. g. 

 Cenito along the Posillipo shore, breeds during the winter months, and that during these 

 months the males never possess the ova in their testes, but at other places, e. g. Torregaveta, 

 I have found O. gammarellus at the same time of year which were not breeding (no females 

 being found with eggs) and a large proportion of the males here had ova in the testes. 



The result is this then , that the males of these species, when breeding is not going 

 on, assume a semi-hermaphrodite condition of a quite indubitable kind which must evidently 

 bear some relation to the metabolic conditions in the body, as the ova always degenerate and 

 a true functional hermaphrodite Sand Hopper has, I believe, never been found. The parti- 

 cular metabolic condition which calls forth the production of these ova is, I think, clearly 

 that condition of adaptive anabolism which we have studied in the infected males under Para- 

 sitic Castration, and in the middle males or males of suppressed sexuality under High and 

 Tow Dimorphism. 



The remarkable manner in which all these facts fit together, presenting us with a 

 theory of the nature of male organization, its essential difference to the female and in what 

 this difference lies, and of the relation which subsists between male sexuality and the general 

 growth and nutrition of the body, may give us some hope that the nature of Sex, that problem 

 which lies at the very basis of organic life change, is open to the methods of scientific 

 analysis. 



>j This inference has been subsequently confirmed. 



