IO4 



NEMERTINEA 



g a end ; and strong muscles unite its pos- 



3 % terior extremity to the sheath a short 



& distance from the posterior end of the 



g | latter. 



| ^ The proboscis seems to be exclusively 



3 f^ a tactile and protective and defensive 



'1 organ, for which functions it is emi- 



o.i nently fitted by the great ease and 



J rapidity with which it is everted or 



| thrust out from the body. It consists 

 J of two distinct regions (Fig. 54, g.p 

 5 g~ and vn.p). In the retracted state the 

 Jg anterior part is a hollow tube with 

 'I I very thick muscular walls made up of 

 ju ~- several layers. At the base of this part 

 " - in many of the Nemertines there is 

 -I ^ situated a sharp-pointed spine project- 

 's I ing forward into the lumen, and several 

 J^-f smaller stylets situated in a pair of 

 | fe vesicles close to the base of the central 



1 ~ 2 spine. The position of the spines in 

 - 2 ^ the everted proboscis is shown in Fig. 

 J 'I ^ 57. The posterior part of the pro- 

 a J g boscis is also a tube, but instead of 

 * J ^ being muscular, its walls are glandular. 

 JT-Ir'l This posterior glandular part is never 



1 f. 2 everted. 



& | ^ The eversion is effected by a turn- 



2 o ^ ing inside out of the anterior part of 

 g>|-| the proboscis (Fig. 54). The process 

 | I J whereby the proboscis is retracted has 

 ' & a been very aptly compared to the effect 

 ' -^.^ which would be produced by the inver- 

 E ^ |, sion of the finger of a glove, accom- 

 l ^ H plished by pulling a string attached to 

 9 & | its tip 011 the inside, the anterior mus- 

 n" | cular part being comparable to the 

 d finger and the glandular part to the 



string. It is thus obvious that in the 

 everted condition the stylet will form the anterior tip of the 



p 



-p.S 



