228 Royal Society : — 



are very long ; and their tails have a spiral movement as well as an 

 undulatory one. They twist into all sorts of loops. 



The muscular tissue of Peripatus is unstriated. 



The development of Peripatus was only partially followed. As a 

 rule, all the embryos found in one mother are of the same age. 

 In some cases slight differences were found, which were very 

 valuable for determining the development of the parts of the 

 mouth. The embryos he coiled up in simple hyaline envelopes, 

 enclosing an ovoid cavity, within the enlargements of the uterine 

 tubes. In the earliest stage observed the embryo had large round 

 cephalic lobes and was without members, but showed distinct seg- 

 mentation 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 antenna?. 



The front members are formed first : they arise as undulations 

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

 further outwards, 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 are the largest at first, but subsequently become the 

 small oral papilla?. 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 

 maxdlse 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 underlip of Scolopendra 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 



