268 
CRUSTACKA. 
clypeus, and apparently formed in the parenchyma, for they were 
not dispersed by the change of tegument, 
Argiilus foliaceus, 3\x\'\r\.e,3\xn., Ann. Mus. d’Hist. Nat. VII, 
xxvi ; Monoculus foliaceus, L. ; Argulus delphinus, Herm. Jun., 
Mem. Apter., V, 3, VI, ii ; Monoculus gyrini, Cuv., Tabl., 
Elem, de I’Hist. Nat. des Anim., p. 454 ; 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 unguicu- 
lated ; the others divided into a greater or less number of pinnulse 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 of 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 liave 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. G^n(5r. des Sc. Phys., vol. Ill, p. 343, Brussels, is an extract 
from the observations of Dr. Surriray on the fcetus of a species of Caligus which he 
believes to be the elongatus, and which is very common on the operculum of the 
Esnx 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 tliesc observations we might be induced 
