Myriapods are hatched at different stages of development. The Chilognatha have only three appendages, which are so little developed that they are only small shapeless stumps, while {67}the Chilopoda have the full number of legs in some cases; in others only a small number of legs, but yet more than the three pairs of legs of the Chilognatha, and fully developed instead of stump-like. The eyes are usually developed late in the life of the young animal. The bursting of the egg-shell is assisted in some Myriapods by a special kind of spike on the back part of the head. The Fig. 40 shows a young Chilognath which has just burst the shell and come into the outer world. It is still surrounded with a membrane which has been formed by its skin or epiblast within the egg. One eye-spot has been formed. [Illustration: FIG. 40.—Young _Julus terrestris_ just hatched.] Fig. 41 shows a longitudinal section through the young Chilognath shown in Fig. 40, and the next (Fig. 42) a transverse section through the same. In comparing the two Figs. 41 and 42 it must be remembered that they are _sections_ in different planes through the animal shown in Fig. 40, and therefore they only show a small portion, a thin slice, of the organs. [Illustration: FIG. 41.—Longitudinal section through late stage: _Sup.oe.gl_, First appearance of brain; _st_, mouth; _pr_, anus; _mesen_, gut; _n_, nerve cord; _n.gang_, nerve ganglion; _mem.ex_, membrane surrounding the animal; _v.f_, ventral flexure; _mes_, mesoblast cells. (Heathcote, Post. Emb. Dev. of _Julus terrestris_.)] {68}The first appearance of the mouth appendages has been already mentioned, and these are shown in Fig. 43, where the small stumps that later on change to jaws are shown. The figure shows the head of a young Chilognath seen from the lower side, and the second pair of stumps fuse together later on and produce the broad plate already mentioned as the characteristic mouth appendage of the Order. [Illustration: FIG. 42.—_G_, gut; _Malp.T_, Malpighian tube; _N.C_, nerve cord; _Tr.I_, deep invagination by which the tracheae are formed; _y.s_, yolk spherules still present; _L_, first appearance of legs; _S.S_, part of mesoblast. (Heathcote, Post. Emb. Dev. of _Julus terrestris_.)] [Illustration: FIG. 43.—Under surface of the head of a young _Julus terrestris_: _pro.m_, rudimentary jaws; _Deut.m_, rudimentary mouth plate; _an_, antennae.]