348 
IN'SECTA. 
the sternal part of each segment, and communicate internally with a 
double series of pneumatic sacs strung together like a rosary, extend- 
ing along the body, from which proceed tracheal branches that ra- 
mify over the other organs. According to an observation of Straus, 
the sacs or vesicular trachea are not, as usual, connected with each 
other by a princiijal trachea. 
In the environs of Pisa, where M. Savi collected the preceding 
facts, the nuptial season of the common lulus commences near the 
end of December, and terminates about the middle of May. The 
male organs of copulation, in this species, 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 Glomeres and 
lull, behind the origin of the second pair of feet, exhibit two convex 
mammillae, which appear to characterize this sex; that of the males 
also consists of two mammillae, but each of them is terminated by a 
scaly and twisted hock. 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 ani- 
mal 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 the assertion of De Geer, who 
says that he only found three pairs and eight annuli in the young 
animal — but it is certain that this change of which Savi speaks is 
really the first ; and should we not, on the contrary, rather presume 
that these young individuals do not suddenly pass from a state in 
which they exhibit 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 obser- 
vations of the Swedish Reaumur confirm these gradual transitions ? 
Be this as it may, the first eighteen pairs of feet, according to Savi, 
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 afterwards 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, 
