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Show 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., wh~ 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 0~ 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. Neithet· of the feet with cups; those of the anterior pair unguicu. lated; the others divided into a greater or less number of pinuulre or membranous leaflets. A considerable portion of the body is not covered by the shell, aqd is usually terminated posteriorly by two long threads, and sometimes by fin-like or styliform appendages( 1 ). The vulgar name of fish-louse, by which they are collectively designated, announces their habits to be similar to those of the Arguli and other Siphonostomre. 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, ~xternal 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. Muller 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 respiration, like the terminal filaments of the abdomen of an Apus(2). (1) The interval also frequently exhibits other, but smaller or much Jess salient appendages. (2) In the Ann. G~n6r. des Sc. Phys., vol. III, p. 343, Brussels, is an extract fro~ the observations of Dr Surriray on the fcx:tus of a species of Cali gus which be believes to be the elongatus, and which is very common on the operculum of the Esox be/one. 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 fcx:tus, 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 extemal oviducts: but is there PJECILOPODA. 151 Some of them whose feet are free, and (the two last excepted) annexed to the anterior part of the body-Cephalothorax, Lat.covered by the shield, in which some of the posterior feet are furnished with numerous and pennated threads, and in which the siphon is not apparent, have the abdomen naked above and terminated by two long threads, or as many stylets; they compose the subgenus CALI Gus, properly so called.-Caligus risculus, Leach( 1 ). In all others, the superior surface of the body is imbricated, or that portion of the body is enclosed in a kind of case formed by the la'st feet which resemble membranes and fold over it. Of these latter, there are some whose antennre never project like little claws, whose feet are free, and whose last ones do not envelope the body like a membranous case. They form the following subgenera. PTERYGOPODA, Lat.-Nogaus? Leach. Where the posterior extremity of the body is terminated by two kinds of fins; where the under part of the post-abdomen or of the second division of the body, not covered by the shield, is furnished with pinnated or digitated feet; and where there is a distinct proboscis or rostrum(2). PANDARus, Leach. Two threads at the posterior extremity of the body; the first and fifth pairs of feet unguiculated, and the remainder digitated; no apparent siphon(3). DINEMouRA, Lat. Two long anal filaments and an apparent siphon; the two anterior feet unguiculat~;!d; the two following ones terminated by 'two long toes, and the remainder membranous leaflets( 1 ). no mistake in this ? I have studied these same organs in various specimens-preserved in spirits, it is true-but could never discover any body whatever. (1) Caligus piscinus, Lat.; Cal. curtus, MUll. Entom., XXI, 1, 2; MO'floculus piscinua, L.; Cal. Mulleri, Leach; Desmar., Consid., L, 4; found on the Cod. The Oniacua lutosw, Slabber, Encyclop. Method., Atl. d'Hist. Nat. CCCXXX, 7, 8, from the fin-like appendages of its tail, seems to indicate a separate subgenus. The Binocle a queue en plumet, Geoff., might be placed in it. (2) A single living species found on the Shark. See the genus Nogau.s, Desmar., Consid., p. 340. (3) Pandarus bico/Qr, Lea&ch; Desmar., L., 5; Pandarus Boscii, Leach, Encyc. Brit. Suppl. I, xx. }'or th .. other species, see Desmar., lb., p. 339. (1) Caligus productus, MUll., Entom. XXXI, 3, 4; Monoculus salmoneu.a, Fab. |