Miscellaneous. 165 



Metazoon the nuclei of the germ-cells, so here the so-called nucleoli 

 come into intimate contact, and the result here as there is aa inter- 

 mixture of different germ-plasmas. With Weismanu, I am con- 

 vinced that this result is the purpose of both sexual fecundation 

 and conjugation, and the condition of the variability of the indivi- 

 duals, without which species-production would bo impossible. 



"With the certainty that in the phenomena of conjugation the 

 essential thing is the exchange of nuclear substance in the two con- 

 jugated individuals, we stand on much more solid ground for the 

 explanation of these processes, and may for the future drop all more 

 indefinite notions. Among these we have as the chief the most 

 generally entertained opinion, which indeed is apparently supported 

 by facts, that the purpose of conjugation is the rejuvenescence of 

 Infusoria exhausted by continual division *. — Berichten der natiirf. 

 OesellscJiaft zu Freiburg I. B. Band ii. (188G) Heft 1. 



On the Injlnence of certain RhizocephaToiis Parasites upon the External 

 Sexual Characters of their Host. By M. A. Giard. 



Most of the Ehizocephala parasitic upon the Decapod Crustacea 

 occasion the atrophy of the genital glands of their host without the 

 external sexual characters of the latter undergoing the least modifi- 

 cation. Thus Sacculina triangularis, Anderson, which occurs pretty 

 frequently at the Poulignan, and more rarely at Concarneau, upon 

 Platycarcinus pagunis, affects both males and females, widely pro- 

 jecting on each side of the narrow tail of the former, while it is 

 entirely protected by the broader appendage of the other sex. 



But this is not always the case, and in some instances the parasite 

 by its presence causes modifications so extensive that the infested 

 males become like the females in types in which sexiial dimorphism 

 is most strongly marked. A very dis<:inct examjjle of this is furnished 

 by Sacculina Fraissei, sp. nov., a parasite of Stenorhynchus phalan- 

 gium, Penn. This Sacculina, indicated but not described by Fraisse 

 in the Bay of Naples, occurs commonly at Concarneau, in the Bale 

 de la Forest. We may estimate at one iu fifty the number of 

 Stcnorhgnchi infested by this llhizocephalau. As in the case of the 

 Sacculina of Carcinus mcenas, the parasite arrives at its complete 

 formation during the period of reproduction of the crab, that is to 

 say, in the present case, during the months of June and July. 



Sacculina Fraissei is easily distinguished from other species of the 

 same genus by its external form and its organization. It is entirely 

 concealed in the kind of box formed by the tail of the crab and the 

 sternal plastron. Its outline is heart-shaped. Thecloacal aperture 

 is nearly sessile, irregularly triangular in the young. The chitinous 

 ring which surrounds the peduncle is very simple and not strongly 

 marked. The peduncle is short ; the roots are thicker and more 

 irregularly ramified than those of S. Carcini ; the collateric glands 

 are well developed and situated upon the sides and towards the 

 upper third of the height. The orientation is the same as that of 

 Sacculina carcini. The nearly spherical testes are situated at the 



* The author promises a more detailed paper with figures. 



