THE DEVELOPMENT OF THE EXTERNAL FORM OF THE BODY, 



181 



to the modified method of development within the uterus, the close 

 connection of the embryo with the wall of the uterus leading to the 

 later development of its external form. In P. novae-zeal andiae the 

 limbs are to be found while the two halves of the germ-band are still 

 far apart (Fig. 86), and in P. capensis also they appear early. 



The embryo, at an early stage, becomes curved, and, as the body 

 elongates, its posterior end becomes rolled up ventrally (Fig. 85, 

 p. 177), this being determined either by its position within the egg- 

 shell or (secondarily as in P. Edwardsii) within the brood-cavity. 

 In P. Edicardsii the posterior end forms several coils. The posterior 

 extremity of the embryo of P. capensis is also at first bent in towards 

 the ventral surface of the body (Fig. 85), but subsequently this pos- 

 terior region grows parallel with that surface, the bend being retained 

 at the middle of the body, and the embryo lies in the egg-envelope 

 in such a way that the anterior and posterior halves of the body are 

 almost parallel to one another, the head touching the posterior end. 



In P. novae-zealmidiac, in a stage earlier than that illustrated in Fig. 86 A 

 and B, a ventral flexion apparently occurs in the embryo, the latter consequently 

 assuming a curved form, but it soon straightens again to some extent, and 

 retains the form shown in Fig. 86 A and B (L. Sheldon, No. 12, Pt. L). 

 Here also the two halves of the germ-band are at first very far apart, as may 

 be seen from Fig. 86 A and B. 



rf_. 



\ 



\ 



J 



Op. 



In keeping with the unspecialised 

 external form of the adult Peripatus, 

 the further development of the embryo 

 is very simple, and, apart from the 

 anterior region of the body, presents 

 no specially noteworthy features. The 

 formation of the limbs continues in the 

 manner above described (Fig. 91), until 

 the final number is reached. Where 

 the two halves of the germ-band lie far 

 apart, as in P. novae-zeatandiae, they 

 eventually shift together to form the 

 ventral surface, a process which is 

 assisted by the gradual absorption of 

 the yolk. The dorsal surface at the 

 same time assumes its final shape. 



The annulations of the body, and the papillae which are seen on its 

 surface in the adult condition, appear in the form of folds and slight 

 elevations of the epidermis. 





Fig. 90. — Anterior part of an embryo 

 of P. Edwardsii, dorsal aspect (after 

 v. Kennel), at, antenna ; k, max- 

 illary segment ; op, segment of the 

 oral papillae ; p, first adult trunk 

 5i ginent ; x, prominence in front of 

 the antennal rudiment (c/. pp. 18'* 

 and 1S7). 



