184 



ONYCHOPHORA. 



lies directly in front of the sharp edge of the stomodaeal aperture, 

 and thus, when that aperture is walled in by the lateral folds, shifts 

 with it into the cavity thus formed (Fig. 94 B). The folds then 

 unite in front of this unpaired papilla, the upper lip of v. Kennel 

 (Fig. 95). The posterior unnotched continuations of the lateral 

 folds form the posterior boundary of the buccal cavity, on the 

 floor of which the primitive aperture of the stomodaeum now lies 

 surrounded by the jaws and the upper lip. 



From the above it will be seen that, in Peripatm, there are three 



distinct apertures, each of which in 

 turn must be regarded as the oral 

 aperture : (1) the primitive blastoporic 

 mouth (Fig. 84 D, m), which persists 

 in the adult as the opening between 

 the oesophagus and the stomach-intes- 

 tine ; (2) the stomodaeal mouth (Fig. 

 93, m), which in the adult puts the 

 buccal cavity into communication with 

 the pharynx; and (3) the external 

 opening of the buccal cavity, which 

 functions as the mouth in the adult, 

 and is formed by the concrescence of 

 two ectodermal folds. 



Fig. 93. — Cephalic part of an embryo 

 of P. capensis (after Sedgwick). 

 at, antenna ; /, oral fold ; k, jaw ; 

 m, stomodaeal aperture ; op, oral 

 papillae ; sp, aperture of the sali- 

 vary gland ; vo, aperture of the 

 ventral organ. 



The shifting forward of the lateral folds towards the oral aperture has also 

 caused the ventral organs of the first two segments to shift into the buccal 

 cavity (Fig. 94 A, voj and vo 2 ). "We shall refer to these again later. Another 

 pair of folds exactly like those which have walled in the oral aperture' are 

 sometimes present, according to v. Kennel, on the outer side of the lateral 

 folds, hut these do not seem to be of constant occurrence. They, however, 

 seem further to support the view, which appears very probable, that the folds 

 found near the mouth of Peripatus do not represent limb-rudiments, as has 

 been conjectured by Moseley. 



The third pair of limbs are less closely connected with the mouth 

 than are the jaws, for while they also shift towards the oral aperture, 

 they remain outside the lips of the buccal cavity (Fig. 95, opi). Apart 

 from the fact that no chitinous hooks develop on them, they retain 

 to a greater degree the character of limbs. They are early distin- 

 guished from the other limbs by their greater development (Fig. 

 91 B, op). These limbs are known as the oral papillae, at the tips 

 of which the slime-glands open. In the adult, these papillae lie 

 as far forward as the jaws (Fig. 95), and the segment to which they 

 belong must therefore be reckoned as a cephalic segment. Three 



