104 



NEMERTINEA 



*3 bo 







int o r r- 



end ; and strong muscles unite its pos- 

 terior extremity to the sheath a short 

 distance from the posterior end of th< 

 latter. 



The proboscis seems to be exclusively 

 a tactile and protective and defensiv 

 organ, for which functions it is emi- 

 nently fitted by the great ease an< 

 rapidity with which it is everted 01 

 thrust out from the body. It consists 

 of two distinct regions (Fig. 54, g.\ 

 and m.p). In the retracted state the 

 anterior part is a hollow tube with 

 ' I very thick muscular walls made up of 

 j. several layers. At the base of this part 

 JJ in many of the Nemertines there is 

 -lg situated a sharp-pointed spine project- 

 's Is 4 ing forward into the lumen, and several 

 l^-l smaller stylets situated in a pair of 

 -s vesicles close to the base of the central 

 o spine. The position of the spines in 

 r * & the everted proboscis is shown in Fig. 

 57. The posterior part of the pro- 

 boscis is also a tube, but instead of 

 s 

 ^ being muscular, its walls are glandular. 



This posterior glandular part is never 

 everted. 



The eversion is effected by a turn- 

 ing inside out of the anterior part of 

 the proboscis (Fig. 54). The process 

 whereby the proboscis is retracted has 

 & & been very aptly compared to the effect 

 ^ which would be produced by the inver- 



CO V o 



CD -~ 



0) v-f 



09 Ph 



ill 



| ^ 1, sion of the finger of a glove, accom- 

 | c; i , plished by pulling a string attached to 

 9 & its tip on the inside, the anterior mus- 

 w f s 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 



