284 



ZOOLOGY 



SECT. 



pr 



T>r 



?n 



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. 



APPENDIX TO PLATYHELMINTHES. 



CLASS NEMERTINEA. 



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

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



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 

 FiG.|233.-Diagr am of the organs of a aspect. Near it in front (rarely 



Nemertine, from below, a. anus ; br. united With it) there IS an Opening 

 f_ brain ; div. caeca ; long. ne. longitudinal , i i i -i -i 



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



I Hubrechtf ; ** (After 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, where its edges are continuous 



