CHAPTER VI 



PHYLUM NEMERTINEA 



THE Nemertines belong to that category of animals popularly 

 styled "worms"; that is to say they are long, soft-bodied animals, 

 without limbs or appendages of any kind, which progress by un- 

 dulatory movements of the body. Most Nemertines are marine, 

 living under stones and amongst seaweed ; a few are found in 

 fresh water and one or two species are terrestrial. 



They swim in a graceful, undulating fashion, but they are much 

 more sluggish in their movements than Annelida. It is a common 

 and characteristic sight to see an isolated contraction passing 

 slowly back . along the body. Some species are minute, others, 

 e.g. Linens marinus, attain a length approaching 100 ft., and are 

 perhaps the longest animals known. 



The ectoderm consists of long, narrow, ciliated cells. In this, 

 they resemble the Turbellaria, but they differ from the latter 

 animals profoundly in the structure' of the alimentary canal. This 

 canal is it is true straight and unbranched, but it differs from the 

 alimentary canal of all Coelenterata and of Platyhelminthes in 

 possessing two openings one in front, the mouth, for taking in 

 food, and one behind, the anus, for rejecting undigested material. 

 For most of its course the alimentary canal is sacculated; that is 

 to say, it is produced at the sides into a series of short broad 

 pouches; otherwise it is not differentiated in any way. 



The most characteristic organ of the Nemertine is the pro- 

 boscis. This is a long tube lying above the alimentary canal, 

 ending blindly behind, and opening to the exterior in front. The 

 proboscis is a part of the outer skin invaginated, and when retracted 

 it is surrounded by a closed space lined by a well-defined epithelium 

 called the proboscis-sheath. This space contains a watery fluid, 

 and its wall beneath the epithelium possesses powerful circular 

 muscles. When these contract the proboscis is partially forced 

 out of the sheath by being turned inside out and consequently 

 s. & M. 8 



