448 



CRUSTACEA. 



Fig. 20.— Diche 

 lestiuu sturionis. 



Dichelestium, of the younger Hermann, has the body narrow, elongated, slightly dilated in front, and composed 

 of seven segments, the anterior being larger, rhomboidal, and composed of the head and part of the thorax united. 

 It supports, 1, four short antennae, the lateral ones being filiform, 7-jointed, and the intermediate pair advanced 

 like short arms, 4-jointed, with the last in the form of a didactyle claw ; 2, a siphon on its under-side, mem- 

 branous and tubular ; 3, three kinds of mis-shapen palpi (two many-cleft legs ?) on each side, situated on an ele- 

 vation ; and, 4, four feet fitted for prehension, of which the two anterior are terminated by several unequal- 

 sized, toothed hooks, and of which the second pair are terminated by a strong hook. Each of the second and third 

 segments supports a pair of legs formed of a joint terminated by two kinds of lingers, toothed at the tip. To the 

 fourth segment is attached a fifth pair of legs (the last), being in the form of simple, oval, and immovable vesicles, 

 which Hermann regarded as ovaries rather than legs. The hind segment is flattened, and terminated by two minute 

 vesicles. The eyes are not distinct. 



D. sturionis, Hermann, is about seven lines long. The legs are only seen when the animal is re- 

 versed. It [is found upon the Sturgeon], into the skin of which it insinuates itself deeply. Hermann 

 found as many as twelve on one fish. Two or three of this number, males probably, were one-third 

 shorter than the others. They twist themselves about with great rapidity. They affix themselves 

 very firmly by their frontal claws. 



Nicothoe, Aud. and M. Edwards, terminates the class of the Crustacea, and is distinguished 

 by its anomalous form. With the naked eye, it appears to consist only of two large lobes 

 united together, somewhat like a horse-shoe, inclosing two others ; but, with the microscope, it 

 appears that the two large lobes are two large lateral expansions of the thorax, having the appear- 

 ance of wings, nearly oval, and directed backwards, and that the two others are external ovaries, 

 like those of the female Cyclops, attached by a small peduncle to the base of the abdomen. The 

 body consists of, 1, a distinct head, supporting two eyes widely apart ; two short, lateral, seta- 

 ceous, Il-jointed antennae ; the mouth formed of a circular opening, performing the office of a cup, 

 accompanied, on each side, by maxilla-shaped appendages (fore-legs) ; 2, a thorax, composed of 

 four segments, having, on the under-side, five pairs of legs, the two anterior terminated by a strong 

 hook, and the eight others composed of a large joint, terminated by two nearly cylindrical, sub- 

 equal branches, each composed of three joints ; and, 3, an abdomen, pointed behind, composed 

 of five joints, the first largest, and supporting the pair of large, oviparous sacs, the last terminated by two long 

 bristles. The lateral expansions appear to be only the excessive developement of the fourth aud last segments of 

 the thorax. 



N. astaci (Aud. and M. Edwaids, Ann. Sci. Nat. 1826) is half a line long, and about three lines wide, including 

 the thoracic prolongations. It is of a rosy hue, with the lateral expansions yellowish. It attaches itself firmly to 

 the branchiae of the lobster, burying itself deeply in the filaments of these organs. They occur in small quantities, 

 and only upon certain individuals. All the specimens hitherto observed were furnished with these ovaries. It is 

 probable, however, that, previous to becoming fixed, they are able to swim ; and that, at that period, their thoracic 

 lobes had not acquired their ordinary developement. 



[The animals composing the Siphonostoma are, comparatively speaking, the most imperfectly 

 organized of all the Crustacea; a peculiarity probably resulting, at least to a certain degree, 

 from their parasitic habits. Latreille, in his introductory observations, had noticed the rela- 

 tion of some of these animals with the Lernacae, but doubted the existence of any actual affinity 

 between them. Two Prussian naturalists, however, Dr. Von Nordmann, and my friend Bur- 

 meister, have more recently published some elaborate memoirs upon these animals, which 

 completely prove their relation : this is especially the case with such genera as Achtheres, 

 Ergasilus, &c, which have not only articulated bodies and jointed members, but their young 

 are active animals, very closely resembling the young of many of the more imperfect Bran- 

 chiopoda. Dr. Burmeister, whose memoirs are jjublished in the 1/th volume of the Nova 

 Acta Cces. Nat. Curios., accordingly unites these together into one group, which he calls 

 Schmarotzerkrebse (Siphonostoma, Latr.) divided into five families : 1, Penellina, com- 

 prising the genera Lernaa, Lerneeocera, Penicidus, and Penella j 2, Lern^eoda, genera, 

 Anchorella, Tracheliastes, Brachiella, Lernceopoda, Achtheres, Basanistes, Condr acanthus, and 

 Lemanthropus j 3, Ergasilina, genera, Nicothoe, Ergasilus, Bomolochus, Lamproglene, 

 Anthosoma, Dechelestium, Nemesis j 4, Caligina, genera, Cecrops, Chalimus, Caligus, Pan- 

 darus, and Dinematura ; 5, Argulina, consisting of the single genus Argulus.*~\ 



* [I regret that want of space prevents me from giving an account 

 of the very elaborate details relative to these singular animals, which 

 are thus rendered doubly interesting from being upon the confines of 



two of the great animal subkingdoms. M. Kollar has also nubli 

 the descriptions of some new species ia the last number ol lue .- :i 

 Trumactiuns.^ 



lied 



