Miscellaneous. 315 



year put forward the hypothesis that the fact noticed by Eathke 

 "was no doubt correct only in appearance, and that if no male Palae- 

 mons are found to harbour Bojrj/ri this is because the atrophy of 

 the testes in the infested males produces as a consequence an arrest 

 of development of the external sexual characters *. I have since 

 been able to verify the correctness of this supposition both in our 

 European prawns infested by Bopyri and in Fala^mon ornatiis of the 

 Brussels Museum infested by Prohopyrus asceudens. The large size 

 of the last species renders the proof more easy. Besides the posi- 

 tion of the genital apertures there are, in the Palsemons, a certain 

 number of secondary sexual characters which have been well indi- 

 cated by Grobben and J. V. Boas, namely : — 



1. The males are smaller than the females. 



2. The thoracic chelae are generally longer in the males. 



3. The inner ramus of the first pair of abdominal feet is much 

 more developed in the male than in the female and differently 

 fringed. 



4. The second abdominal foot bears on the inside of the inner 

 ramus, between this and the retinaculum (^appendix interna, 

 Boas), a styloid copulatory appendage furnished with stiff 

 setse {app>endix mascidina. Boas). 



5. The branch of the first antenna which bears the olfactory 

 setae is larger in the male than in the female, and this abso- 

 lutely and not only relatively to the size of the body ; the 

 olfactory setae are also more numerous. 



We may add to the preceding characters a peculiarity indicated 

 by E. von Martens, and which is of very great practical value, 

 namely that in the females the free apace between the bases of the 

 fik^th thoracic feet is much larger than in the males. 



The characters derived from the size and from the form of the 

 chela^ are of relative value. If we compare suitably selected series 

 of individuals it is easy to find males of smaller size and with 

 shorter chelae than certain females. It is therefore not surprising 

 to find that these characters disappear completely in the castrated 

 males. But with the exception of the distinctions derived from 

 the position of the genital apertures and the distance of the feet of 

 the fifth thoracic pair it is easy to ascertain that the other sexual 

 characters also become attenuated, or even disappear, in the infested 

 males. The inner ramus of the first abdominal foot is, perhaps, a 

 little larger than in the female, but at any rale much smaller than 

 in the normal male. On the second jiair the appendix mascnUna 

 is generally wanting. In one word, the general aspect is so pro- 

 foundly modified that, w ithout careful examination, the infested 

 male would certainly be determined as a female. Even the amouut 

 of separation of the coxae of the fifth pair of thoracic feet and the 



* Bull. Soc. Sei. de la France et de la Belgique, 1887, p. 12 et seqq. ; 

 translated in ' Annals,' ser. 6, vol. xix. pp. 325-345. 



