NEMATHELMINTHES. 343 



Fain. Lineidae. Ganglion elongated. The head has deep slits on either side. 

 Lutfiix nuirinnn Mont.. L. Icngissimus Sim. (sea long-worm, Jiarhixin, anglicn 

 Oerst.. Ncmertes Jlnrliixii Cuv.). grows to a length of 15 feet and more. 

 English coast. C'eirbrafulus marginatux = Mcckella xomntotomux F.S. Lkt., 

 Adriatic and Mediterranean. Micrwa fasciolata Ehrbg., North Seas to the 

 Adriatic. 



Fain. Cephalotrichidae. Cephalic slits and lateral organs are wanting. Head 

 not distinct, very long and pointed. Ceplialirtltrlr hiwulata Oerst. Sund. 



Malacobdella yroxxu, 0. Fr. Mull. Body broad and flat, with posterior sucker. 

 Is parasitic in the mantle cavity of various Mollusca. as My a, Ct/j)rina, etc. 



CLASS II. NEMATHELMIXTHES. 



Round worms with tubular or filiform bodies. The cuticle is fre- 

 quently rinyed. The anterior pole is either armed with hooks or 

 provided with papilla. The sexes are separate. 



The unsegmented body is rounded, more or less elongated, tubular 

 or filiform, and both ends are, as a rule, tapered off. Appendages 

 are always wanting, as are, with few exceptions, movable bristles. 

 On the other hand, special organs for attack and attachment, such 

 as teeth and hooks, are not unfrequently present on the anterior 

 end of the body ; and in some cases small suckers, which serve for 

 attachment during copulation, may be developed on the ventral 

 surface. As a rule, the integument possesses a cuticular layer of 

 relatively considerable thickness, and a well developed muscular 

 layer, which permits not only of the body being knotted, curved, and 

 bent, but, in the thin filiform Nematoda, of undulatory movements. 

 The body cavity is enclosed by the muscular body wall, and con- 

 tains the blood fluid and the digestive and generative organs. 

 Blood vessels and respiratory organs are wanting. A nervous 

 system is, however, always present. Of sense organs simple eyes 

 are not unfrequently present in the free living forms. The sense 

 of touch is probably distributed all over the surface of the 

 body, particularly on the anterior end, especially when papillae 

 and lip-like prominences or bristles are found on it. While in the 

 Acanthocephala mouth and alimentary canal are completely absent, 

 the Nematoda possess a mouth placed at the anterior pole of the 

 body, an oesophagus, and an elongated straight digestive canal, which 

 usually opens by the anus on the ventral surface near the pos- 

 terior end of the body. The excretory organs have various forms, 

 and always differ considerably from those of the Platodes. In the 

 Nematoda they consist of paired canals, which open by a common 

 pore and lie in the so-called lateral lines. In the Acanthoce- 



