268 CRUSTACEA. 



clypeus, and apparently formed in the parenchyma, for they were 

 not dispersed by the change of tegument. 



Argutus foliaceus, Jurine, Jun., Ann. Mus. d'Hist. Nat. VII, 

 xxvi ; Monoculus foliaceus, L.; Argidus delphinus, Herm. Jun., 

 Mem. Apter., V, 3, VI, ii ; Monoculus gyrini, Cuv., Tabl., 

 Elem. de I'Hist. Nat. des Anim., p. 4.^4 ; Ozolus gasterostei, 

 Lat., Hist., Nat. des Crust, et des Insect., IV, xxix, 1 — 7 ; Des- 

 mar., Consid., L. ; Louse of the Stickleback, Baker, Micros., II, 

 xxiv. This species, the only one of the genus that is known, 

 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. Herman, 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 divided into 

 five rings, but slightly distinct on the back. 



Caligus, Mull. 



Neither of the feet , with cups ; those of the anterior pair imguicu- 

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

 membranous leaflets. A considerable portion of the body is not 

 covered by the shell, and is usually terminated posteriorly by two 

 long threads, and sometimes by fin-like or styliform appendages.* 



The vulgar name oi fish-louse, by which they are collectively desig- 

 nated, 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 Jurine, Jun., 

 and such also is the opinion of his father, that they serve for respi- 

 ration, like the terminal filaments of the abdomen of an Apusf. 



* The interval also frequently exhibits other, but smaller or much less salient 

 appendages. 



f In the Ann. G6n6r. des So. Phys., vol. Ill, p. 343, Brussels, is an extract 

 from the observations of Dr. Surriray ou 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 fnetus, very different from the mother, 

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



