Miscellaneous. 387 



For one crab bearing a Sacculina in good health, we find four or 

 five loaded with a bundle of agglutinated mussels and Molgidce. 

 On removing these foreign bodies we constantly find either the 

 flabby and half- destroyed skin of the Sacculina, or merely a chitinous 

 ring, the last vestige of the presence of the parasite. 



Molgula social is is rendered the more formidable because it retains 

 among its aggregations the mussels, calcareous sponges (Sycortis 

 quadrangulata), Bryozoa, &c. fixed under the tail of the crustacean. 



From these facts we may deduce: — 1, the existence of a uro- 

 delous larva in Molgula socialis, which is verified by experimental 

 embryogcny ; 2, the presence of Cancer mcenas in the laminarian 

 zone, which the ascidian in question inhabits ; 3, the possible co- 

 existence of the Molgula and Cancer mamas, and even a sort of 

 mutual dependence of these animals upon each other ; and, 4, the 

 incorrectness of the opinion of those zoologists who have supposed 

 that the absence of a certain species of Molgula in the zone of 

 C. mcenas was due to the presence of that crustacean. 



On the shores of Brittany, where it has not to dread the presence 

 of Molgula socialis, the Sacculina is very common, and the numerous 

 companions that it may have do not seem to incommode it much. 

 We find, in fact, under the tails of the Crabs infested by it : — 

 1. Synascidia (Botry2lusviolaceus,Poluclinum sabulosum) ; 2. Ihyozoa 

 (Pedicellina, Tubulipora serpens, Cellcpora pumicosa) ; 3. Annelides 

 (Spirorbis) ; 4. Calcispongia) (Sycandra coronata and ciliata) ; and, 

 5. Vorticellae and numerous and varied Infusoria. 



In the interior of the mantle we frequently meet with Copcpod 

 Crustacea, nearly allied to those which frequent the brancbia of 

 the Ascidia, and especially a species related to Lichomolgus, and 

 remarkable for the dilatation of the prehensile antenna of the 

 male. 



But the most interesting parasite of the Sacculina is an Isopod 

 Crustacean of the family Bopyridae, and of the genus Crgploniscus, 

 F. Miiller. Two species of this genus are already known, viz. 

 Cryptoniscus pygmceus (Liriope pygmaa), ltathke, parasitic on Pel- 

 togaster p>aguri(m the European seas), a\\(\ Cryptoniscus planario'ides, 

 F. Miiller, parasitic on Peltogaster purpureas (in the seas of Ame- 

 rica). The Cryptoniscus of Sacculina, which I propose to call C. 

 larvceformis, differs greatly from the preceding in external form, at 

 least as regards the female sex. The male, which is met Avithin the 

 ovigerous cavity of the Sacculina, closely resembles those of the other 

 Cryptonisci. The female is fixed to the base of the peduncle of the 

 Sacculina. Externally it presents the appearance of the hinder part 

 of the body of the larva3 of the Lamellicorn Coleoptera. It is more 

 than 1 centimetre in length ; its colour is whitish ; the integument 

 is slightly diaphanous, and shows in its interior a yellowish red mass. 

 This reddish mass is regarded by F. Miiller as a liver in Cryptoniscus 

 planario'ides ; but as it is greatly developed before oviposition, and 

 much reduced, on the contrary, when the ovigerous sac is full, it 

 appears to me to have some relation to the generative functions, 

 and may perhaps act the part, of a vitelligene, or accessory gland of 

 the ovary. 



