NEMERTINES 



305 



A brief survey will now be made of these thirteen phyla, but 

 many particulars regarding them will be found in other parts of 

 this work. 



NEMERTINES (NEMERTEA) 



Although the worm-like forms which belong here have a 

 wide distribution, and are particularly common between tide- 

 marks on almost all coasts, they are nevertheless practically 

 unknown except to the professed naturalist, and have received 

 no common names. There are some forty British species. The 

 vast majority are marine, and either shore or shallow- water forms, 

 but they are also represented in fresh water and even on land. 

 They have been given here the first place among Invertebrates, 

 in deference to the views of many zoologists, in whose opinion they 

 come near to the Protochordates. 



The body of a typical Nemertine (fig. 177) is cylindrical, and 

 presents no trace of segmentation. It may be only a small 

 fraction of an inch in length, or in other cases many yards long. 

 A common British form (Linens marinus) is one of the species 

 which are extremely elongated, and it may not infrequently be 

 found under stones, with its slimy black body twisted up into a 

 complicated coil. Other species may be more or less brightly 

 coloured. 



The mouth is a small oval opening on the under side of the 

 head end, while the aperture of the intestine is at the extreme 

 tip of the tail. Close examination will show that above the 

 mouth on the front end of the body there is a small pore, and 

 in a living specimen a narrow thread may sometimes be seen 

 to shoot out from this pore, through which it can again be 

 drawn back into the body. This thread is known as the 

 proboscis, and, as described elsewhere, it is used as a means of 

 killing or paralysing the marine worms upon which a Nemertine 

 chiefly feeds. When within the body it is enclosed in a special 

 sheath which overlies the digestive tube. The proboscis is 

 hollow, and the way in which it is protruded and again drawn 

 back may be understood by taking the somewhat hackneyed 

 illustration of a glove with one finger. If this finger be pulled 

 back into the main glove by turning it outside inwards, we shall 

 have a rough model of the proboscis when lying within the body. 



VOL. I. 20 



