446 
CRUSTACEA. 
Fiff. 24. — Argulus foliaceus. 1, 
the animal mag-nified ; 2, one 
Argulus, Mull., at first named by me Ozoliis, but not sufficiently described. The younger Jurine subsequently 
examined the species which is the type of the genus, with the most scrupulous attention, observing it in all its 
stages. The shield is oval, notched posteriorly, covering the body, with the exception 
of the posterior extremity of the abdomen, and supporting, on a triangular frontal 
space termed the clypeus, two eyes, four very minute antennae, nearly cylindrical, 
placed in front — of which the superior, very short and 3-jointed, have, at the base, a 
strong, toothless, recurved hook, and of which the inferior are 4-jointed, with a small 
tooth ui)on the basal joint. The siphon is directed forwards. The legs are twelve in 
number. The two anterior are terminated by a large limb, circularly dilated at the tip, 
and striated and toothed at the edge; exhibiting, on the inside, a kind of rosette, 
formed by the muscles, and seeming to act as a sucking-cup. Those of the second pair 
are fitted for prehension, with the thighs thick and spinose, and the tarsi composed of 
oTthe iarge ‘an teHoV' sucking" three joiiits, the last of which is terminated by two hooks. Tlie other feet are termi- 
lengtiu natural j^ated by a swimmeret formed of two fingers, or elongated pinnulae, fringed with bearded 
threads. The third pair of legs has an extra finger, but which is recurved. The last 
pair of legs is attached to that part of the body which is disengaged behind the shield, or the tail. The abdomen — 
regarding it as the part of the body extending backwards between the ambulatory feet, the beak, and a tubercle 
inclosing the heart— is entirely free from the place of its insertion, without distinct articulations, and terminates 
immediately behind the tw o last feet in a kind of tail, in the shape of a rounded, deeply-notched plate, without 
hairs at the tip. It is a kind of swimmeret. The transparency of the integuments permits the heart to be per- 
ceived. It is situated behind the base of the siphon, lodged in a solid tubercle, semitransparent, and in the fonn 
of a single ventricle. 
The eggs are oval, and of a milky white colour : they are attached by gluten to stones or other hard substances, 
either in one or two rows, to the number of from one to four hundred. The eggs hatch about thirty -five days after 
they are deposited ; and the young ones, on bursting forth, are only three-eighths of a line long. Their general 
form is similar to that of the adult state, but the locomotive organs exhibit essential differences. Muller described 
the animal in this state as a distinct species, named Argulus Charon. Four long oar-like arms, two placed before 
and tw o behind the eye, each terminated by a brush of flexible hairs, w hich the animal moves simultaneously, and 
by the help of which it swims easily, v/ith a jerking motion, arise from the anterior extremity of the body. The 
rudiments of the antennae are also visible. Tlie tw'O large sucker-like feet are replaced by two strong legs elbowed 
near the extremity, and terminated by a strong claw, with which the animal affixes itself to fishes. Of the other 
legs which appear in the adult state, those only of the second and third pairs, or the two ambulatory feet, and the 
two anterior natatory legs, are the only ones which are developed and free : the following are, as it were, lapped up, 
and applied against the abdomen. The first moulting, wffiich is effected by means of a rupture of the skin on the 
under-side of the body, having taken place, the oar-like limbs disappear, and all the natatory legs become disen- 
gaged. Three days afterwards, the second moult takes place, which does not produce any important change ; but 
at the third moult, which takes place two days aftei-wards, we begin to perceive the formation of the suckers of the 
fore-legs. At the fourth moult, wdiich also takes place at the end of two days, these legs have assumed the sucker 
shape, preserving, however, the terminal hook. At the end of six days, there is another change of the skin, w'heu 
the organs of generation become apparent ; but there still remains another moult, retarded for six days, before 
these animals are fitted for reproduction. Thus the period of their metamorphoses extends to twenty-five days. 
They have then, however, attained only half their size. Other moultings, which take place evei*y six or seven days, 
are necessary for their aiTiving at their full growth. Jurine asserts that the females do not become parents with- 
out the presence of the males. Those which he kept isolated died of a disease which manifested itself in numerous 
brown globules, arranged in a semicircle towards the posterior part of the clypeus. 
The only species of this genus known [to Latreille] {Argulus foliaceus, Jurine ; Monoculus foliaceus, Linn. ; 
Argulus delpliinus, and A. Charon, Muller ; Monoculus Gyrini, Cuvier ; Ozolus Gasterostei, Latr.) attaches itself 
to the under-side of the body of the young of Frogs, Sticklebacks, &c., and sucks their blood. Its body is flattened, 
of a greenish-yellow colour, and about two lines and a half long. The younger Herman, who has well described 
this crustaceous insect in its perfect state, and who cites a manuscript of L. Baldaner, a fisherman of Strasbiirg, 
of the date of 1666, where the same animal is figured, says that, in the neighbourhood of that city, it is only found 
upon the trout, which it destroys, especially in fish-ponds. It is also found upon the perch, pike, and carp. He 
says it has never been found upon the gills of the fish. This animal turns itself about 
in the water in a similar manner to the Gyrini. He says its body is divided into five 
somewhat indistinct segments along the back. 
[A most elaborate memoir, containing the description of Argulus Catostomi, an 
American species of this genus, has recently been published by Messrs. Dana and 
Herrick, in Silliman’s Journal.'] 
Caligus, Miill., are destitute of the sucker-like feet. The anterior legs are furnished 
with hooks : the others are divided into a greater or less number of pinnulae, or are in 
the form of membranous leaflets. The shell leaves a considerable part of the body ex- 
posed, which is terminated posteriorly, in the majority, by tw o long filaments, and in 
others by appendages in the form of fins or styles. The space between these appendages Yig. 2i.—Caiigus pischius, I.inn. 
also often exhibits various other minute appendages. ""g °f ie|l’ 
The name of fish-lice, under which these animals are collectively known, indicates 
that their habits are the same as those of the other Siphonostoma. Many naturalists have considered the tubular 
