OCR Text |
Show 248 INSI<~OTA. four feet are even ~ntirely fr~e to their origin, where they merely adhere to thc11· respecuve segments by a median or sternal line. The last two or three rings are without feet. A series of pores is observed on ear.h side of the body, which were considered as stigmata, but, according to Savi, they are simply designed to afford a passage to an acid fluid of an extremely disagt·eeable odour, which appears to serve as a means of defence; the respiratory apertm·es, for whose discovery we are indebted to him, are situated on the sternal part of each segment, and communicate internally with a dou. ble series of pneumatic sacs strung together like a rosm·y, extending along the body, from which proceed tracheal branches that ramify over the other organs. According to an observa· tion of Straus, the sacs or vesicular trachea are not, as usual, connected with each other by a principal trachea. In the environs of Pisa, where M. Savi collected the pre. ceding facts, the nuptial season of the common Iulus com. mences near the end of December, and terminates about the middle of May. The male organs of copulation, in this spe· cies, are situated under the sixth segment, but they do not appear in this form till the individual has attained the one· third of its full size; until this epoch, that place is occupied by a pair of feet (the fifteenth), which is always found there in the females ; in the latter, the orifice of the sexual organs is between the first and second segment. Some female Glo· meres and Iuli, behind the origin of the second pair of feet, exhibit two convex mammillre, which appear to characterize this sex; that of the males also consists of two mammillre, but each of them is terminated by a scaly and twisted hook. These Insects, in coitu, erect the anterior extremities of their bodies, and place them in contact, face to face, twining round each other inferiorly. The body of the new-born animal is reniform, perfectly smooth, and destitute of appendages. Eighteen days after, it undergoes its first change, and then for the first time assumes the form of the adult, still, however, having but twenty-two segments; the total number of feet also amounts to twenty-six pairs. Savi appears to contradict MYRIAPODA. 249 the assertion of De Geer, who says that he only found · three pairs and eight annuli in the young animal-but is it certain that this change of which Sa vi speaks is really the first, and should we not, on the contrary, rather presume that these young indi~iduals do no~ suddenly pass from a state in which they exhibtt no locomotive appendages to one where we find them possessed of twenty-six pairs, or in a word, that previous changes of tegument, which have escaped the notice of Savi, have taken place and successively developed this number of feet? Do not the observations of the Swedish R.eaumur confirm these gradual transitions? Be this as it may, the first eighteen pairs of feet, according to Sa vi, alone serve for locomotion ; at the second change we observe thirty -six pairs, and at the third, forty -three ; the body then consists of thirty segments. Finally, in the adult state, the male has thirty nine, and the female sixty-four; two years after~·ards they again experience a change, and then only do the genital organs make their appearance. From the moment of their birth, which occurs in March, until November, at which time M. Savi terminated his observations, these changes take place about once a month. In their exuvire, we find even the lining membrane of the alimentary canal and trachere. The organs of the mouth were the only parts that Sa vi could not discover(!). These Insects feed on dead and decomposed animal and vegetable matters; they deposit in the ground a large number of eggs. According to the system of Linnreus they form but one genus, that of IuLus, Lin. . Which we divide as follows: Some have a ct·ustaceous body without terminal appendages, and antenn~ enlat·ged near the end. (l) See Uullet. Gener. et Univers. of the Baron Ferussac, Decemb., 1823. The ~bservations of Savi, an extract of which is contained in this work, were published tn a memoir, entitled "Osservazioni per servire allft. storia di una specie di Julus communissima," Bologna, 1817. The same savant published another in 1819 on the JulU8 /fltidi~aimm. Vot. III.-2 G |