Page:Wood 1865 - The Myriapoda of North America.djvu/7

142 a series of small plates anterior to the sternum, representing the two parts of the primitive sternum (Fig. 2, s), and the two episterna (Fig. 2, e), as well as the epimeral plates.

The legs contain each a coxa (Fig. 2, d), a femur, b, a tibia, t, a tarsus, g, and metatarsal joints, m, n. The coxæ are generally small, except those of the posterior pair of legs, which are often very large, and are known as the lateral anal appendages. Among the Cermatiidæ and Lithobiidæ, however, they all attain to a considerable size. The metatarsal joints vary very much; in the genus Scolopendra there are but two to each leg, whilst among the Cermatiidæ there are a great number.

The head in the Chilopoda is composed of eight subsegments consolidated into two or more segments, as was first shown by Mr. Newport. The first segment is styled the cephalic. It reaches its maximum size in the Cermatiidæ, in which it is the most prominent part of the body, supporting a pair of very large compound eyes, and almost completely concealing the strikingly atrophied basilar segment. Traces of the division into the four subsegments, that existed during embryonic life, are occasionally met with, especially among the Lithobiidæ, but the embryological labors of Mr. Newport have shown conclusively that it is so formed. The head in the Scolopendridæ has, in addition to the cephalic segment, another one of variable size; this is the basilar. It is also found well developed in all the other families except the Cermatiidæ. Near its anterior border there is often found a deep crescentic groove; the portion separated by this from the main body, is called the prebasilar fold or subsegment. In the genus Mecistocephalus this subsegment is entirely separated from the rest, its scutum existing as a small plate immediately posterior to the cephalic, and is there called the prebasilar. In the other genera of the Geophilidæ this is wanting, but there exists posteriorly another segment, answering to the posterior portion of the basilar of the Scolopendridæ. It is the subbasilar of Newport. The under surface of the head, comprising as it does the organs of nutrition, is much more complicated than the upper, and, in order to show the relations of parts more clearly, I will trace them out minutely in the genus Scolopendra, where perhaps their analogy is most easily discovered.

On examining the under side of the head of a specimen of the genus Scolopendra, we will find a band constituting the most anterior portion, with which the antennæ partially articulate; this band I take to be the anchylosed primitive sterna and episterna of the first cephalic subsegment, of which the antennæ are the appendages. Just posterior and inferior to the eyes, we will see what is apparently an inversion of the cephalic scutum, but closer examination shows it to consist of two small plates, the superior exterior (Fig. 3, e), uniting with the scutum by suture, the inferior interior (Fig. 3, h) approximating to the other plate; the first of these is the atrophied episternum, the other the primitive sternum of the second cephalic subsegment. United with this sternum by