TUEBELLAKTA. 11 



one of the best known species (Nemertes Borlasii) is said to be 

 capable of stretching itself to fuUy eight times the length of the 

 body as it occurs in the ordinary state of rest ; and in tliis case, 

 therefore, the animal, which usually appears to be some five or six 

 feet long, is capable of assuming, at any time, a length of at least 

 forty or fifty feet. Professor Rymer Jones measured a specimen 

 which was twenty-two feet when dead, and this worm, he felt 

 certain, " might have been extended to four times the length" when 

 ahve, thus giving a total of no less than eighty- eight feet ! Be 

 this as it may, the Nemertidse very closely resemble the common 

 tapeworms— or Cestodes properly so called — not only by their 

 band-hke forms, but more particularly by their tendency to display 

 transverse rugae, which, as before remarked, acquire a certain degree 

 of regularity. These animals, however, are furnished with a large 

 protrusible proboscis and a simple digestive tube, the latter, accord- 

 ing to some authorities, not terminating by any anal outlet. On 

 the other hand, Delle Chiaje, Huschke, Rathke, Oersted, and Yon 

 Siebold, consider that the intestinal canal opens by a distinct 

 anus at the posterior extremity of the body. Duges and Oersted 

 describe a vascular system (in Polystemma) consisting of longi- 

 tudinal vessels which anastomose in the region of the head; a 

 similar arrangement being also observed by Quatrefages in Nemertes 

 mandilla, where the vessels are three in number, two lateral and 

 one median. Milne-Edwards states that the blood is colourless, 

 but, according to Yon Siebold, the Nemertians have red blood. 

 This is a point which should not be left undecided by those who 

 have opportunities of examining these worms in the living state. 

 Rathke and Quatrefages speak of the sexes as distinct, and the 

 former has carefully described the nervous system as it occurs in 

 Borlasia. He states that it consists of a pair of cephalic ganglia, 

 which send off" two long, lateral, non-ganghonic ventral cords, in 

 addition to several small nerve-branches to the front of the head. 

 Some of these are distributed to the eye-specks, which vary con- 

 siderably in number in the different Nemertian genera; other 



