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Show 210 A ltACUNJDES. FAMILY II. PYCNOGONIDES. The trunk, in this family, is composed of four segmen~ occupying nearly the whole length of the body and terminat~ at each extremity by· a tubular joint, the anterior of which is the largest, sometimes simple, and sometimes accompanied by che1icerro and palpi, or only one kind of these organs, that constitutes the mouth(l ). There are eight legs in both sexe~ formed for running, but the female is furnished with two ad· ditional false ones, placed near the two anterior, and solely destined to carry her eggs. The Pycnogonides are marine animals(2), analogous either to the Cyami and the Caprellre, or to the Arachnides of the genus Phalangium, where Linnreus placed them. Their body is commonly linear, with very long legs, composed of eight or nine joints, terminated by two unequal hooks which appear to form but one, and the smallest ofwhich is cleft. Thefi~t segment of the body, which replaces the head and mouth, forms a projecting tube, cylindrical or in the form of a trun. cated cone, with a triangular aperture at its extremity. The cheliccrro and pal pi are placed at its base. The former are cylindrical or linear, simply prehensile, and composed of two joints the last of which is a forceps, the inferior finger or the one that is .fixed being sometimes shorter than the other. The palpi are filiform, and consist of five or nine joints, with a terminal hook. Each of the following segments, the last excepted, bears a pair of legs(3); but the first, or the one arti· ( 1) On the siphon of a large species of Phoxichilus brought from the Cape of Good Hope by the late M. Delalande, I observed longitudinal sutures, so that it appears to me to. be composed of the labrum, ligula, and two jaws, all soldered together. In tbts case the palpi belong to the jaws. (2) According to Savigny they form the transition from the Jlracltnide8 to the Crustacea. We place them here, but with some hesitation. (3) M. Milne Edwards, who bas investigated the anatomy of these animals on the living subject, has told me that in the interior of these organs he observed TR-:\CIIEA RliE. 211 1 t d with the mouth, has a tubercle on the back, on which cu a ~aced two eyes on each side, and beneath, in the females are! p two additional small folded legs, bearing the eggs which 00 yc, o11ected around th. em 1· n one or two peI I ets. Th e Ia st are ent is small, cylindrical and perforated by a little orifice settghme extremity. N o vesti· ge of sti·g mata can b e percei·V e d . a They are found among marine plants, sometimes under stones near the beach, and occasionally also on the Cetacea. · PvcNOGONUM, Brun., Mull., Fab. The chelicerre and palpi wanting; length of the feet hardly greater than that of the body, which is proportionably thicker and shorter than in the following genera. They live on the Cetacea( 1 ). PnoXICIIILus, Lat. Thepalpi wanting, as in the Phoxichili; but the lE>gs are very long, and there are two chelicerre(2). NYMPHON, Fab. The Nymphones resemble the Phoxichili in the narrow and oblong form of their body, the length of their legs, and in the presence ofchelicerre; but they have, besides, two palpi(3). bteral expansions ot' the intestinal canal, or ca:ca. I have, in fact, observed traces of them under the form of blackish vessels, in various Nymphones. This induces me to believe that these animals respire by the skin, a character by which we might form them into a particular order, and one perhaps intermediate between the Arachnides and Apterous Insects of the order of the Parasita. (1) MUll, Zoo). Dan., CXIX, 10-12, the female. Found on our coast by MM. Surirey and d'Orbigny. (2) Refer to this genus the Pycnogonum .Ypinipes of Othon Fabricius, his variety of the P. grossipes, without antenna:; the Pltalangiwrn aculeatt~~m,· the .Ypinosum Montag., Lin. Trans.; the Nymplwn Jemoratum of the Acts of the Soc. of Nat. Hi st. of Copenhag., 1797; the Nymplwn hirtum, J<'ab., which perhaps does not differ from the Phal. spinipes and spinost~m above quoted. (3) Pycnogonum grossipes, Oth. Fab.; MUll., Zool. Dan., CXIX, 5-9, the fe· male; to compare with the Nymph. gracile and femoratum, Leach, Zool. Miscell., XIX, 1, 2. Ilis genus .IJ.mmotltea-.9.. carolinensis, lb.-differs from Nymphon in the chelicer~ which are much shorter than the mouth, the first segment or radical joint being very small. The pal pi consist of nine joints, while those of the Nymphoneshave but five. In this genus, as well as in Pltoxicltilus and Pycnogom1m, the ~econd joint of the tarsi is very short. The tubercle on which the eyes at·c placed, ~ sometimes situated on an elevation which projects above the bnse of the antenor segment or the mouth. |