The mouth parts consist of two minute pairs of appendages, the anterior pair toothed and the posterior pointed. The body is rather narrower in front; the segment behind the head has one pair of legs, the second, third, fourth, and fifth behind the head two each. The posterior legs are the longest; the genital organs open at the base of the second pair of legs, between these and the third pair. The manner of breathing is as yet unknown, tracheae not having been discovered. _Pauropus_ at first looks most like a Chilopod, but differs from that Order— 1. In the form of the antennae. 2. In the absence of poison claws and in the form of the mouth parts. {63}3. The opening of the generative organs being in the front part of the body. It differs from Chilognatha in the following respects:— 1. The legs are not of equal length, the posterior legs being the longest, as in Chilopods. 2. The mouth parts differ from those of Chilognaths almost as much as from those of Chilopods. 3. The form of the antennae. Only a few Pauropoda have been discovered as yet. EMBRYOLOGY. The preceding account of the anatomy of Myriapods would be incomplete without some reference to the wonderful manner in which the different organs of the body are built up; the whole of the complex organism proceeding by a gradual and regulated process of development from a simple cell called the ovum derived from the female body, and united with a cell from the male body (called the spermatozoon). I hope to be able to give my readers some idea of the interest which the pursuit of the difficult study of embryology adds to anatomy, by offering us a key to the interpretation of the relations between our knowledge of the forms at present living on the earth and those which, we learn from Palaeontology, have inhabited our planet in past ages. [Illustration: FIG. 36.—Young ovum of _Julus terrestris_: _nucl_, nucleolus; _nu_, nucleus; _R_, first appearance of yolk; _F_, follicle cells.]