6. Special Reference of the phenomena of Parasitic Castration to High and Low Dimorphism. Q3 



Since this chapter was in great part written, Mr. F. A. Potts of Trinity Hall, Cam- 

 bridge has studied at Naples the effect of Peltogaster on Eupagurus meticulosus. His results, 

 which will shortly be published, are in their main features strikingly confirmatory of my 

 own on Sacculina, but in many exceedingly interesting features the hermit-crabs show a diver- 

 gent kind of reaction to their parasites to that which I have found in the spider crabs. By 

 his permission I may state that infected male hermit-crabs assume in various degrees the 

 secondary sexual characters of females, whereas the modification which females may undergo 

 can be interpreted as a mere arrest of development and not in any way as a definite 

 acquisition of male characters. He is therefore of the same opinion as myself that 

 the females are incapable of assuming any definitely male character under the influence of 

 parasitic castration. 



In a large prop ortion of infected males the reduced testes contain a number 

 of small ova, while in infected females no sign of spermatozoa is ever found. 



This important discovery is completely in accord with the recovered male crabs found 

 by me exhibiting an hermaphrodite gonad, except that in the hermit-crabs the ova are pro- 

 duced in the testes before the Peltogaster is got rid of and the crab has begun to recover; in 

 other words the reaction of the gonad occurs precociously. 



I have chosen out two of the most important results from Mr. Potts' work which are 

 directly confirmatory of my conclusions, but for many other points of almost equal importance 

 a reference must be made to his full paper, which will shortly appear in the Quarterly Journal 

 of Microscopica! Science. 



Chief Literature referring to Parasitic Castration. 



1. Giard, A., De l'influence de certains parasites Rhizocéphales sur les caractères sexuels extérieurs de leur 



hòte. in: C. R. Acad. Se. Paris Tome 103 p. 84 1886. 



2. , La castration parasitaire. in: Bull. Se. Dép. Nord (2) 10. Année Tome 18 p. 1 1887, 



3. , Sur la castration parasitaire chez V Eupagurus berrihardus et chez la Gebia stellata, in: C. R. 



Acad. Se. Paris Tome 104 p. 1113 1887. 

 4. , Sur. un Copépode [Cancerilla tubulata) parasite de YAmphiura squamata, ibid. p. 1189. 



5. , Sur la castration parasitaire chez les genres Palaemon et Hippolyte. ibid. Tome 106 p. 502 1888. 



6. — , Sur la castration parasitaire du Lychnis dioica par YUstilago antherarum. ibid. Tome 107 



p. 757 1888. 



7. , Sur le Peroderma cylindricum 1 Copépode parasite de la Sardine, ibid. p. 929. 



8. , Sur les parasites Bopyriens et la castration parasitaire. in: C. R. Soc. Biol. Paris Tome 4 1887. 



9. , La castration parasitaire (Nouvelles Recherches). in: Bull. Se. Dép. Nord (3) Tome 1 



p. 12 1888. 



10. , Sur la castration parasitaire de VHypericum perforatum par la Cecidomyia hyperici et par 



VErysippe Martii. in: C. R. Acad. Se. Paris Tome 109 p. 324 1S89. 



