270 



NEMERTEA. 



R 



mud, but the smaller species swim freely. There are also forms 

 which live on land (Geonemertes), fresh-water forms (species of 

 Tetrastemma), and a pelagic form (Pelagonemertes). Certain species 

 form tubes and passages which are lined by a slimy secretion. The 

 food of the larger species principally consists of tubicolous worms, 



which they extract by 

 their proboscis. There are, 

 however, parasitic (or com- 

 mensal) Nemertines, which 

 infest Crustacea, or live on 

 the mantle and gills of 

 Mollusca. In this case 

 they are, like the Hiru- 

 dinea, furnished with a 

 posterior sucker (Malacob- 

 della). 



Order 1. 

 PROTONEMERTINI. 



Am 



FIG. 224. Later stage of Pilidium, with tuft of cilia 

 and enclosed Nemertine (after O. Biitschli); Oe 

 oesophagus ; D alimentary canal ; Am amnion ; 

 R rudimentary proboscis of the Nemertine ; So 

 lateral pit. 



The cerebral ganglia and 

 lateral nerves are outside the 

 dermal muscles, either in the 

 ectoderm or beneath the dermis. 

 The body-wall consists of the 

 ectoderm, a dermis, an external 

 circular and an internal longi- 

 tudinal layer of muscles, between which is usually interposed a diagonal layer. 

 The mouth is behind the brain. There is no caecum. The proboscis is without 

 stylets. 



Fam. 1. Carinellidae. The lateral organs have the form of epithelial pits 

 or canals, which only exceptionally perforate the dermis and penetrate into 

 the brain ; they have no relation to the lateral vessels. There is no dorsal 

 vessel. The brain and lateral nerves lie in the epithelium or beneath the 

 dermis. The dermis is homogeneous and has a gelatinous appearance. Carinella 

 Mclntosh. 



Fam. 2. Hubrechtidae. The lateral organs are spherical structures which 

 lie deep within the body-wall and project into the lateral vessels. Brain and 

 lateral nerve-cords lie beneath the dermis, which is reticular. There is a dorsal 

 vessel. The excretory organs constitute a richly-branched canal - system. 

 Hubrechtia Burger. 



Order 2. MESONEMERTINI. 



The lateral nerves lie in the dermal muscular layer. Body- wall as in Order 1. 

 Mouth behind the brain. No caecum. The proboscis is without stylets. 



Fam. 1. Cephalothricidae. The lateral nerves are in the longitudinal 

 muscles. Lateral organs, and cephalic slits absent. Carinoma Oudemans ; 

 Cephalothrix Oersted. 



