150 CRUSTACEA. 



attaches itself to the under part of the body of the tadpoles of 

 Frogs, of that of the Stickleback or Gasterosteus, and sucks its 

 blood. The body is flattened, of a light yellowish green colour, 

 and about two lines and a half in length. Hermann, Jun., who 

 has well described this Argulus in its perfect state, and who 

 quotes a manuscript of Leonard Baldaneur a fisherman of Stras- 

 bourg, dated 1666, in which the same animal is figured, says, that 

 in the environs of that city it is seldom found, except on the 

 Trouts, and that it frequently kills them, those especially which 

 are kept in ponds; it is also found on the Perch, Pike, and 

 Carp. He has never found it on the gills. It has a habit of 

 whirling round like the Gyrini. He says that the body is di- 

 vided into five rings, but slightly distinct on the back. 



Caligus, Mull. 



Neither of the feet with cups; those of the anterior pair unguicu- 

 lated; the others divided into a greater or less number of pinnulse or 

 membranous leaflets. A considerable portion of the body is not co- 

 vered by the shell, and is usually terminated posteriorly by two long 

 threads, and sometimes by fin-like or styliform appendages(l). 



The vulgar name of fish- louse, by which they are collectively de- 

 signated, announces their habits to be similar to those of the Arguli 

 and other Siphonostomse. Several naturalists have considered the 

 tubular threads at the posterior extremity of their body as ovaries; 

 I have sometimes found ova under the posterior and branchial feet, 

 but never in these tubes. Besides, external oviducts thus prolonged 

 are never met with except in females whose eggs are to be deposited 

 in deep holes and cavities now this is not the case with the Caligi. 

 Miiller and other zoologists have remarked that these Crustacea 

 erect and agitate the appendages in question. We believe with Ju- 

 rine, Jun., and such also is the opinion of his father, that they serve 

 for respiration, like the terminal filaments of the abdomen of an 

 Apus(2). 



(1) The interval also frequently exhibits other, but smaller or much less salient 

 appendages. 



(2) In the Ann. Gner. des Sc. Phys., vol. HI, p. 343, Brussels, is an extract 

 from the observations of Dr Surriray on the foetus of a species of Caligus which he 

 believes to be the elongatus, and which is very common on the operculum of the 

 Esox belone. That gentleman informs us that by pressing the two caudal threads 

 of the animal in question, a number of transparent and membranous ova were ex- 

 truded, each of which contained a living foetus, very different from the mother, 

 and of which he gives a description. From these observations we might be in- 

 duced to conclude that these threads are a kind of external oviducts: but is there 



