EXCRETORY AND GENERATIVE SYSTEMS IO9 



a direct communication, by means of open connexions with the 

 lacunar blood spaces, is said to occur. 



Silliman 1 in Tetrastemma aquarum dulcium describes the 

 excretory vessels as ending in numerous capillary branches, at 

 the blind terminations of which cilia are present. He states that 

 there is no important difference between the excretory systems 

 of Ehabdocoeles and Nemertines. 



Biirger, 2 as the result of recent investigations on the excre- 

 tory system in Nemer tines, finds that the minute branches end 

 in flame-cells (Fig. 56, B) lying on and among the blood-vessels, 

 but having no open connexion with them. 



Generative System. The Nemertines are for the most part 

 dioecious, only a few certainly hermaphrodite species having been 

 described, e.g. Tetrastemma (" Borlasia ") kefersteinii Mar. 3 



The generative products in both cases are contained in sacs 

 (Figs. 52, 53, g) which lie in the lateral region of the body 

 between the pouches of the alimentary canal. The ova and 

 spermatozoa are conveyed to the exterior by short ducts. Most 

 species are oviparous, though a few viviparous species are known 

 (e.g. Prosorlwchmus claparedii). 



Classification. Nemertines were divided by M. Schultze 4 

 into : 



1. Enopla, in which the proboscis is armed with stylets. 



2. Anopla, in which the proboscis is unarmed. 



Although this classification was fairly correct as far as it 

 went, since many other distinctive features were correlated with 

 the presence or absence of armature in the proboscis, still there 

 are several primitive forms belonging to the Anopla, which 

 possess characters such as render it necessary to class them 

 together in a separate group. 



For this reason Hubrecht divided the Nemertinea into three 

 Orders Hoplonemertea, Schizonemertea, Palaeonemertea ; the 

 first of these Orders corresponding with the Enopla, and the 

 other two with the Anopla. 



1 Zeitschr. wiss. Zool. Bd. xli. 1885, p. 48. 



2 Ibid. Bd. liii. 1892, p. 322, and Fauna und Flora G. von Neapel, 22 

 Monogr. 1895. 



3 Ann. Sci. Nat. (5) vol. xvii. 1873. 



4 Zeitschr. wiss. Zool. Bd. iv. 1853, p. 178. 



