Miscellaneous. 387 



For one crab bearing a Saceulina in good health, we find foiir or 

 five loaded with a bundle of agglutinated mussels and Molgulce. 

 On removing these foreign bodies we constantly find either the 

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

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



Mohjula socialis is rendered the more formidable because it retains 

 among its aggregations the mussels, calcareous sponges (Sycortis 

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



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

 delous larva in ^lohjula socialis, which is verified by experimental 

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

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

 existence of the Molgida and Cancer mcenas, 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 MoJgula in the zone of 

 C. mcencts 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 Saceulina 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. Syuascidia {Botryllusviolaceus,Polyclinuin sahulosuni); 2. Bryozoa 

 {Pedieellimt, Tubuliiyora serpens, CeUepora pumicosa) ; 3. Annelides 

 (Spirorhis) ; 4. Calcispongia) (Sycandra coronata and eiliata); and, 

 5. YorticelliB and numerous and varied Infusoria. 



In the interior of the mantle we frequently meet with Copepod 

 Crustacea, nearly allied to those which frequent the branchia of 

 the Ascidia, and especially a species related to LicJiomoJi/us, and 

 remarkable for the dilatation of the prehensile antennae of the 

 male. 



But the most interesting parasite of the Saceulina is an Isopod 

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

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

 Cryptoniscus pyymceus {Liriope pygmcen), Ilathke, parasitic on Pel- 

 togaster paguri (in the Eurojjean seas), and CrypAoniscus plana rioides, 

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

 rica). The Cryptoniscus of Saceulina, 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 with in the 

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

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

 Saceulina. Externally it presents the appearance of the hinder pai't 

 of the body of the larvae of the Laraellicorn 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 

 planarioides ; but as it is greatly developed before oviposition, and 

 much reduced, on the contrary, when the o%-igerous 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. 



