1874.] and Development of Peripatus capensis. 347 



all the embryos found in one mother are of the same age. In some 

 cases slight differences were found, which were very valuable for deter- 

 mining the development of the parts of the mouth. The embryos lie 

 coiled up in simple hyaline envelopes, enclosing an ovoid cavity, within 

 the enlargements of the uteftae tubes. In the earliest stage observed 

 the embryo had large round cephalic lobes and was without members, but 

 showed distinct segmentation about its middle ; it was coiled up spirally, 

 the head being free, the tail in the axis of the coil. Later on the embryo 

 becomes bent round in an oval, with the tip of the tail resting between 

 the antennae. 



The front members are formed first : they arise as undulations of the 

 lateral wall of the body, which become pushed further and further out- 

 wards, and are at first hollow, formed of two layers of cells, the inner of 

 which is reflected over the intestine. The members form one after 

 another, from the head downwards. A line of segmentation is formed 

 across the body before the pair of members swells out, but disappears as 

 they develop. The wall of the digestive tract is, in the early condition, 

 drawn out laterally at each interspace between the pairs of members, to 

 become attached there to the body-wall. The cephalic lobes early show 

 traces of a separation into two segments, anterior and posterior ; from 

 them, anteriorly, bud out the antennae, which gradually become more and 

 more jointed. The mouth forms before the anus. 



The full number of body-members is very early attained. The second 

 pair is the largest at first, but subsequently become the small oral 

 papillae. The first pair turn inwards towards the primitive mouth- 

 opening, and, developing their claws greatly, form the pair of horny jaws ; 

 these are covered by processes which grow down from the lower part of 

 the head, and which eventually unite with the tissues at the bases of the 

 oral tentacles and form the tumid lips, which, eventually closing in, hide 

 all the parts of the mouth in the adult. The head-processes are probably 

 homologous with the mandibles of higher Tracheata, the horny jaws with 

 the maxillae and the oral papillae with the foot-jaws of Scolopendra ; a 

 regular labrum is formed by a downward growth from the front of the 

 head, but is eventually shut in by the tumid lips. 



It is uncertain whether a corresponding structure beneath the mouth 

 represents the second under lip of Scok.pendra or a true labium. The 

 foot-claws are developed in invaginations of the tips of the ambulacral 

 members. The young members develop five joints each, the typical 

 number in insects, and one which seems to be retained in the adult. 



In the present state of our knowledge concerning the structure of 

 Peripatus, the most remarkable fact in its structure is the wide di- 

 varication of the ventral nerve-cords. The fact was considered re- 

 markable and dwelt upon in all accounts of Peripatus before the exist- 

 ence of tracheae in the animal was known, and when it was thought 



