618 F. A. POTTS. 



degree of modification has been developed. It has been 

 noticed that the effect on the primary characters as one 

 which very often supervenes, and may in fact be general for 

 the whole male sex; while on the other hand individual 

 variation plays a great part in the effect produced on the 

 male secondary sexual characters, which possibly in about 

 a quarter may be entirely null. The correlation which 

 exists between the primary and secondary characters must 

 be of a loose nature, and this fact and more particularly the 

 observation of cases in which modification of the append- 

 ages had begun before the corresponding changes in the 

 gonad, appears to conclusively show that the modifying 

 cause, acting on the secondary sexual characters, is not to 

 be sought specifically in the altered character of a secretion 

 of the gonad, but rather in a more general rearrangement of 

 the metabolism, occasioned by the parasite, which affects 

 both primary and secondary characters. 



SUMMAEY. 



(1) The infection of the hermit crab Eupagurus meti- 

 culosus by the cirripede Peltogaster curvatus has the 

 effect of diminishing immediately the size of the gonads and 

 suppressing their functions. This is probably effected 

 through interference with the general nutrition of the host, 

 and not through direct action on the gonads. 



(2) At an early stage of the external parasitism ova make 

 their appearance in the glandular part of the testis. Experi- 

 ments planned to discover the fate of these ova on recovery 

 of the host from the parasite were not very successful owing 

 to the slow regeneration of the gonad, but it seems probable 

 that they persist and grow. No corresponding changes 

 could be traced in the ovar3\ 



(3) The male secondary sexual characters are stimulated 

 to development towards the female type under influence of 

 the parasitism. There is a complete series between un- 



