5IO J. PERCY MOORE. [Vol. X. 



ing fibres, which traverse the internal cavity of the lips and 

 constitute the chief musculature of these versatile structures. 

 The lips are bounded posteriorly by the muscular jaw pads 

 (Fig. 9, dvt, vm). 



Numerous single and small aggregations of unicellular glands 

 are developed from the epidermis of the margins and internal 

 surfaces of the lips. Such are especially numerous on the inner 

 surface of the ventral lip just anterior to the jaw (Fig. 9, og). 

 In a similar position on the dorsal lip is the supposed salivary 

 gland, sg. 



Immediately posterior to these structures are slit-like dorsal 

 and ventral infoldings of the epidermis and cuticle, bounded 

 behind by a thickened epidermal pad. On the posterior walls 

 of these invaginated pockets, and on the epidermal prominences 

 which follow, the jaws are molded. The cuticle of the invagi- 

 nation gives attachment to the protractor muscles of the jaws 

 (Fig. 9, dp7n and vpm), which are dorso-ventral fibres derived 

 from the anterior face of the muscular jaw pads, in addition to 

 which the ventral jaw possesses, as an accessory protractor, a 

 pair of muscle fibres which arise from the apex of the muscular 

 ridge into which the jaw pad rises, and, curving around an 

 isolated fibre posterior to the mass of the pad, insert into the 

 posterior limb of the jaw, on which they exert a dorsal traction, 

 and consequently move the point of the tooth forward (Fig. 9). 

 The retractor muscles are, particularly in the case of the dorsal 

 jaw, an extremely large and powerful pair of fibres, which 

 spring from the longitudinal muscular coat in the region of the 

 first cephalic constriction, and pass obliquely forward to insert, 

 in the case of the upper jaw, directly on the posterior limb of 

 the jaw plate, and of the lower, into the epidermis and cuticle 

 immediately behind the jaw (Fig. 9, dnn [the anterior index 

 line] and vnn). 



The pad on which the jaws are supported is a powerful 

 muscular apparatus formed of two (a dorsal and a ventral) 

 half disks, each of which consists of four or five semi-circular or 

 semi-lunar muscle fibres piled upon and embracing one another, 

 and meeting those of the opposing half disk in a transverse line 

 (Figs. 9 and 10, dm and V7n). This is set transversely in the 



