284 



ZOOLOGY 



SECT. 



centres (brain) in the scolex of some Cestodes (e.g., Moniezia] 

 tells in favour of the view that the scolex is anterior and 

 corresponds to a head.Jjjf 



APPENDIX TO PLATYHELMINTHES. 



ong.ne 



CLASS NEMERTINEA. 



General Features. The Nemerteans are non-parasitic, un- 

 segmented worms, most of which are marine, only a few forms li ving 



on land or in fresh water. They 

 are commonly looked upon as 

 nearly related to the Turbellaria 

 and were formerly included in that 

 class ; but in some respects they 

 are higher in organisation than 

 the Turbellaria, and they exhibit 

 certain special features distinguish- 

 ing them from the rest of the 

 lower Worms. 



The body (Fig. 233) is nearly 

 always narrow and elongated, 

 cylindrical or depressed, unseg- 

 mented and devoid of appendages. 

 In length it varies from a few 

 millimetres to as much as twenty- 

 seven metres. In some cases there 

 is a short narrower posterior 

 region or " tail " ; a head is rarely 

 marked off from the body proper. 

 The entire surface is covered with 

 vibratile cilia, and frequently the 

 integument is vividly coloured. 

 Gland-cells of the epidermis secrete 

 a mucous matter, which may serve 

 as a sheath or tube for the animal. 

 The mouth (m.) is at or near the 

 anterior extremity on the ventral 

 aspect. Near it in front (rarely 

 united with it) there is an opening 



FIG. 233. Diagram Of the organs of a 

 Nemertine, from below, a. anus ; br. 

 brain ; div. caeca ; long. ne. longitudinal . , , , . , 



nerve-cords ; m. mouth ; n. nephridia ; through Which Can be protruded a 



r -r- i~^. muscular 



or. ovaries ; 

 Hubrecht.^ 



pr. proboscis. 



very long muscular organ, the 

 proboscis (pr.), the possession of 



which is one of the most characteristic features of this class of 

 Worms. The proboscis is hollow ; when extended to its utmost, a 

 part still remains which is not capable of being everted. This 

 hollow tube (Fig. 234) is open in front, wfrere its edges are continuous 



