OCR Text |
Show 246 J, 5ECTA. with facets; the lenses are still larger, rounde1·, and more distinct, in proportion, than those of the eyes of Insects. The stigmata are ft·equently very small, and their number owin to that of the annuli, is usually greater than in the Iatte~ where it never exceeds eighteen or twenty. The number of these annuli and that of the feet increases with age, a charac. ter which also distingnis.hes the Myriapoda from Insects, the latter ab ovo always havmg the number of segments peculiar to them, and all their legs with hooks, or true legs, being dc ·;eioped .at once, either at the sat~1e epoch or when they pass m.to then· pupa s.tate. ~· Sa vi, professor of mineralogy at P1sa, who has pa1d particular atteution to the Iuli, has ob. served, that on leaving the egg they are destitute of these organs : they experience then a true metamorphosis. In some, the male organs of generation are placed immediately after the Reventh pair of feet, on the sixth or· seventh segment of the body, and those of the female ncar the origin of the second feet : in the others the two sorts of organs are situated, ~usual, at the posterior extremity of the body. The po (. tion of the male organs of the first compared with that in which they are placed in the Crustacea and Arachnides, would seem to indicate the separation of the trunk and abdo· ~en : with respect to those in which these organs are poste· r10r, we observe that an inversion of the successive order of the stigmata takes place in an analogous portion of the body of certain species, which appears to announce a similar d~tinction. The Myriapoda live and increase in size longer than other Insects, and; according to Savi, two years are required toren· der the gem tal organs of some (the Iuli) of them apparent. _From this ensemble of facts, we may conclude, that these ammals approach the Crustacea and Arachnides on the one hand, and the Insects on the other; 'but that as respects the prel'ence, form and direction of the brachere, they belong to the latter. We divide them into two families, perfectly distinct both MYRIAPODA. 247 ln their organization and h~bits, and forming two genera according to the system of L1nnreus. FAMILY I. CHILOGNATHA(t). The body genera11y crustaceous and frequently cylindrical; the antennre somewhat thicker near the end or nearly equal, and composed of seven joints; two thick mandibles without palpi, very distinctly divided into two portions by a median· articulation with imbricated teeth, implanted in a cavity of its superior extremity; a species of lip-ligula(2)-situated immediately above, that covers them, is crustaceous, plane, and divided on its exterior surface by longitudinal sutures and emarginations into four principal arere, tuberculated on their superior margin, the two intermediate of which, narrower and shorter, are placed at the superior extremity of another area, serving as a common base : the feet very short, and always terminated by a single hook; four feet, situated immediately under the preceding part, of the form of the following ones, but more closely approximated at base, with the radical joint proportionably longer; most of the others attached in double pairs to a single annulus. The male organs of generation are situated immediately after the seventh pair of feet, and those of the female behind the second. The stigmata are placed alternately, outside of the origin of each pair of feet, and are very small. The Chilognatha move very slowly, or slide along, as it were, and roll themselves spirally or into a ball. The first segment of the body, and in some the following one, is the largest, and has the form of a corselet or little shield. It is only at the fourth, in some, and at the fifth or sixth in others, that th~ duplication of the feet commences; the first two or (1) CHlLOGNATtu, Lat. or the genus luLus, Lin . . (2) The lower lip composed of the two pairs of jaws of the Crustacea, accordtng to Saviguy. |