ANATOMY AND DEVELOPMENT OF PERIPATCTS OAPENSIS. 221 



ing the true mouth-opening, and enclosing in their fusion 

 the jaws. 



The lip is covered by a soft skin, in which are numerous 

 organs of touch, similar to those in other parts of the skin 

 having their projecting portions enclosed in delicate spines 

 formed by the cuticle. The skin of the lips differs, however, 

 from the remainder of the skin, in the absence of tubercles, and 

 in the great reduction of the thickness of the dermis. It is 

 raised into a series of papilliform ridges, whose general form is 

 shown in fig. 5 ; of these there is one unpaired and median 

 behind, and a pair, differing somewhat in character from the 

 remainder, in front, and there are, in addition, seven on each 

 side. 



The structures within the buccal cavity are shown as they 

 appear in surface views in figs. 5 and 7, but their real nature 

 is best seen in sections, and is illustrated by PI. XVI, figs. 11 

 and 12, representing the oral cavity in transverse section, and 

 by PI. XVI, figs. IT and 18, representing it in horizontal 

 longitudinal sections. In the median line of the buccal cavity 

 in front is placed a thick muscular protuberance, which may 

 perhaps conveniently be called the tongue, though attached to 

 the dorsal instead of the ventral wall of the mouth. It has 

 the form of an elongated ridge, which ends rather abruptly 

 behind, becoming continuous with the dorsal wall of the pha- 

 rynx. Its projecting edge is armed by a series of small teeth, 

 which are thickenings of the chitinous covering, prolonged 

 from the surface of the body over the buccal cavity. Where the 

 ridge becomes flatter behind, the row of teeth divides into two, 

 with a shallow groove between them (PI. XV, fig. 7). 



The surface of the tongue is covered by the oral epithelium, 

 in parts of which are organs of special sense, similar to those in 

 the skin j but its interior is wholly formed of powerful muscles. 

 The muscles form two groups, intermingled amongst each other. 

 There are a series of fibres inserted in the free edge of the 

 tongue, which diverge, more or less obliquely, towards the skin 

 at the front of the head anteriorly, and towards the pharynx 

 behind. The latter set of fibres are directly continuous with 



