CHAPTEE VI. 



PHYLUM NEMERTEA.* 



Elongated, vermiform animals witli a ciliated ectoderm, and an 

 eversible proboscis lying in a sheath on the dorsal side of the enteron. 

 With mouth and anus, simple gonads, and a vascular system. Dioecious. 



The position of the Nemerten is difficult to settle. Formerly they were united 

 with the Platyhelminthes, but the presence of an anus, and of a vascular system, 

 and the higher organization of the organs and tissues in general, renders it 

 advisable, for the present at any rate, to place them in a separate phylum, 

 allied to the Platyhelminth phylum but not part of it. It has been suggested 

 that the proboscis of Nemertines is homologous with the retractile anterior part 

 of the body found in some T urbellaria, particularly ProrhyncJms. The general 

 structure of the Nemertine tissues strongly recalls that of Balanoglossus. 



The Nemertea are elongated worms, some of them attaining an 

 immense length, and are found in the sea, in fresh water, and on 

 land. The marine forms are, however, by far the most numerous. 

 They are often brilliantly coloured, and many of them have the 

 power of forming a tube around their bodies by the mucous 

 secretion of the skin. The body is excessively contractile, so much 

 so that a worm which is measured by yards when extended may 

 shrink to a length of as many inches. The mouth is large and 

 placed on the ventral surface of the anterior end of the body. It 

 leads into a straight alimentary canal consisting of oesophagus and 

 intestine. The latter opens posteriorly by a terminal anus, and 

 possesses lateral caeca which are generally, but not always, regularly 

 arranged in pairs ; it also gives off from its front end an anteriorly- 

 directed caecum. 



The most characteristic organ of the group is the proboscis. This 



* W. C. Mclntosh, A Monograph of British Annelida, Ft. 1, "Nemerteans," 

 Ray Society, 1873-4. A. A. W. Hubrecht, " Unters. iib. Nemertinen a. d. 

 Golf v. Neapel," Niederl. Arch. f. Zoologie, 2, 1874. Id., "The Genera of 

 European Nemertines critically revised," Notes from the Leiden Museum, 

 1879-80. Id., "Report on the Nemertea," Challenger Reports, vol. 19, 1887. 

 0. Burger, "Die Enden des exkretorischeu Apparates bei den Nemertinen," 

 Zcit.f. iv. Zoologie, 53, 1891. 0. Burger, "Die Nemertinen," Fauna u. Flora 

 des Golfcs von Neapel, 22, 1895. 



