104 CRUSTACEA CHAP. 



tionately much more highly developed than in the low males. 

 The only difference between the two cases is that whereas in 

 the beetles growth ceases on the attainment of maturity in the 

 low degree, in the Crustacea the low male passes through a 

 period of growth and sexual suppression to reach the high 

 degree of development. 



The condition of the middle-sized males may be looked upon 

 as one of partial hermaphroditism, indications of the female 

 state being found in the flattened chelae and in the reduced 

 state of the testes. This interpretation is greatly strengthened 

 by the state of affairs observed in the life-history of the male 

 Sand-hoppers, Amphipods of the genus Orchestia. 1 In the young 

 males of several species of this genus, at the time of year when 

 they are not actively breeding, small ova are developed in the 

 upper part of the testes of more than half of the male individuals, 

 these ova being broken down and reabsorbed as the breeding 

 season reaches its height. Nor is this phenomenon confined to 

 this genus ; in the males of a number of widely different 

 Crustacea these small ova are found in the testes at certain 

 periods of the life-history (e.g. Asiacus 2 ), when the animal is not 

 breeding. 



The foregoing facts indicate unmistakably that the males of 

 a number of Crustacea under certain metabolic conditions, i.e. 

 when a stage of active growth as opposed to a stage of re- 

 productive activity is initiated, alter their sexual constitution in 

 such a way that the latent female characteristics are developed, 

 and the organism appears as a partial hermaphrodite. In the 

 preceding paragraph we saw that the males of a number of 

 animals, especially Crustacea, react to the metabolic disturbance 

 set up by the presence of a parasite in exactly the same way, 

 i.e. by developing into partial or total hermaphrodites. From 

 these two converging bodies of facts we may conclude, firstly, 

 that sex and metabolism are two closely connected phenomena ; 

 and, secondly, that the male sex is especially liable to assume 

 hermaphrodite characters whenever its metabolic requirements are 

 conservative, assimilatory, or in a preponderating degree anabolic, 

 as when a phase of active growth is initiated, or the drain on 

 the system, due to the presence of a parasite, is to be made good. 



1 C. L. Boulenger, Pro,-. Zool. Soc. 1908, p. -42. 

 2 Gamier, C.R. Soc. Jiiol liii., 1901, ].. 38. 



