A thill layer of (loisn-vential luusclcs (PI. IIT., fios. (i and 

 8) is found limning' along- each side of an intestinal 

 divertitniluni. In some Lineidip a horizontal nuiscle layer 

 runs between the [)ro1)oscis sheath and (esophagus in the 

 mouth region, l)ut this layer does not occur in the jnesent 

 species. The muscle hhres in the head are continuorrs 

 with the outer longitudinal layer. The inner longitudinal 

 and circulai' layers of the trunk are not continued 

 anteriorly beyond the l)rain. In the head, however, aie 

 developed an inner layer of longitudinal and an outei- 

 laver of circular tibies round the rhyiiclioda'uni and 

 cephalic blood lacunie (PI. I., hg. '2). 



rUOHOSClS .\X1) PKOIiOSCIS siik.xth. 



The remaining portion of the muscular system is that 

 in connection with the proboscis and its sheath. These 

 two structures commence at the anterior level of the brain, 

 and their relations to one another and to the rhyncho- 

 dauim may l)est be gathered from a reference to PI. II., 

 fig'. 7. The proboscis sheath consists of a layer of longi- 

 tudinal muscle fibres, surrounded externally by a layer of 

 circular ones, and internally invested by the flattened 

 epltheliiim of its contained cavity, the rhynclioc(elom. 

 In its retracted state the proboscis lies in the last-named 

 cavity, and its outer surface is covered by the rhyncho- 

 (•(elomic epithelium. 



The internal . surface of the piolxtscis (/.r., in tiie 

 retracted state! is lined by the high glaiidulai- probosci- 

 dial epithelium, which is of ectodermal origin, aiul is 

 continuous with the epithelium lining the rhyncho- 

 da'um. In other words, the ca\'ities of the retracted 

 proboscis and the rhynchoda'um aic one and tihe .-ame, 

 whilst that of the rhyiichoc(eloni is entiiel\- closed 

 and separated from the rhynchoda'uni by the attaclimeut 



