2. Effect on the primary and secondary sexual characters. 75 



One of these crabs as I have mentioned had no scar, indicating that a Sacculina had 

 been there, and this crab differed from the other three in its general characters and especially 

 in its large size. This crab is figured Plate 7 figs. 18 and 19. I do not think that there 

 can be any doubt that this crab was once infected and that subsequently it had recovered 

 and gone through several moults so as to lose the scar and to attain to its remarkable size. 

 In any case the occurrence of this crab does not in the least invalidate the conclusions drawn 

 from the other three, because it is certain in them, firstly, that they had been infected by 

 Sacculina and had recovered, secondly that their gonads had been nearly eradicated, thirdly 

 that they had regenerated perfect hermaphroditic gonads. That the large crab figured in 

 figs. 18 and 19 belongs to the same category is, I think, certain from the entire absence of 

 any approach to an hermaphrodite state in any other crab out of thousands examined, apart 

 from the effect of Sacculina. On the other hand an approach to an hermaphrodite condition 

 with regard to external characters is shown in a majority of infected crabs, and the perfect 

 hermaphroditism exhibited by these recovered crabs is the natural culmination of the state. 



In conclusion therefore, Crabs which have been modified externally into per- 

 fect hermaphrodites and have lost internally the differentiated gonads, if they 

 recover, regenerate a perfect h ermaphrodite gonad capable of producing mature 

 ova and spermatozoa. 



2. Crabs experimentally freed from Sacculina in Aquaria. 



After perceiving the remarkable fact that infected crabs on recovery may regenerate 

 a hermaphrodite gonad, I was anxious to test this experimentally with the especial purpose 

 of finding out whether this regeneration onlv takes place in crabs of a particular category, 

 namely in those with perfect external hermaphroditism, as appeared to be the case from the 

 four specimens found in nature. 



During the autumn and winter a large number of crabs, showing every degree of 

 external modification from complete external hermaphroditism to the absence of all modification, 

 were artificially freed of their parasites, and kept in Aquaria until the following summer. 

 Unfortunately the death rate among these crabs was very large, and exceedingly few survived 

 till the summer. Of these however not a single one of the incompletely modified crabs 

 showed any signs in their gonads of hermaphroditism, though in some of them the gonads 

 had evidently recuperated to a large extent; but in one of the crabs which exhibited 

 perfect hermaphroditism externally (i. e. belonged to the crabs described in 

 Section C), a small hermaphrodite gland was present on the left side of the 

 thorax, consisting posteriorly of an ovary containing immature but large ova, 

 and anteriorly of a testis containing a quantity of mature spermatozoa. The 

 testicular tube was continuous with the ovary and at the point of junction ova and sperma- 

 tozoa were lying mingled together. No ducts were present. 



10* 



