684 



VERMES— CLASS NEMEKTJNEA. 



proboacis-sheath — or rather round the proboscis-sheath like a ring, for the 

 right and left halves of the brain are joined together by a transverse band 

 which passes above this sheath. The only other organs that need be noticed 

 are the paired nephridia or excretory organs situated in the front part of the 

 body and the thin blood-vessels, sometimes containing red blood, which lie 

 just above and at the sides of the alimentary canal and unite at the anterior 

 and posterior ends of the body. 



In most Nemertines the sexes are distinct, and, as a rule, the young are 

 produced from eggs that are deposited by the mother either singly or in 

 gelatinous clusters ; some forms, however, such as Monopora iivij:ara, retain 

 the eggs until the development is far advanced and the young aie born alive, 



In many species again, as in Lineus, 

 the young goes through a striking meta- 

 morphosis, the egg giving rise to a free- 

 swimming ciliated larva known as the 

 pllidium and consisting of an upper 

 bell-shaped part, from the lower rim of 

 which spring a pair of lobes. Within this 

 larva the young Nemertine ia gradually 

 formed, and when sufficiently advanced 

 to lead an independent life it breaks free 

 from its pilidium-case and deserts it. In 

 other cases the development is less com- 

 plicated, conditions in different species 

 having been observed, which lead from the 

 complete metamorphosis by means of the 

 pilidiura to the direct development of such 

 species as Tetrasttmma and Malacobdella. 



The class is usually divided into two 

 orders, the Enopla and the Anopla, the 

 difference between the two consisting in 

 the presence of stylets on the proboscis in 

 the former and their absence in the latter. 

 To the Anopla belong auch genera aa Folia 

 and Lineus, and to the Enopla or Hoplonemertinea, Malacobddla, Tetra- 

 slemnui, and Geonemertes. 



All Nemertines appear to be carnivorous, feeding upon annelids or other 

 soft-bodied living organisms. The great majority of the species are marine, 

 occurring for the most part amongst sea-weeda and coral rocks, in shallow 

 water; a genus, however, called Pelagoiumertes is found in the open sea. 

 Of the marine forma Malacobdella, which waa originally regarded as nearly 

 allied to the Leeches, lives parasitically upon bivalved Mollusca of the genera 

 Mya, Venus, and Cypridinu. The genus Tetrastemma is interesting for the 

 reason that some of its species are marine, some fresh water, and some 

 terrestrial, one fresh-water species having been found in England, another 

 (T. aquarum-dulcium) in North America ; the two known land species being 

 from Rodriguez (T. rodericannm) and the Bermudas {T. agrkola). The rest 

 of the land species are furnished by the genus Geonemertes, which has a 

 representative (<?. australicnsh) in Australia, another in New Zealand (G. 

 novw-zelandue), a third in the Pelew Islands (G. palaensu), and a fifth, which 

 has probably been introduced, in Germany ; all these land species are found 

 in damp apots beneath logs, stones, etc. 



Fig. 11. 



Nemertinu Worm. — Lineus marinus 



(with proboscis protruded). 



If, Land Planarian (^Bipaliuin 



kewense). 



