166 INVERTEBRATE MORPHOLOGY. 



in reality a portion of the coelom separated off for a special purpose, and 

 other instances bearing the same significance will be noticed later. 



The reproductive system differs from that of the other 

 Platyhelminths iu its much greater simplicity, no vitellaria or 

 shell-gland being present, and furthermore the Nemerteaus 

 are almost without exception of separate sexes. The ovaries 

 (Fig. 84, ov) or testes are present in considerable numbers, 

 one lying in each interval between two lateral diverticula of the 

 intestine, so that they partake in their arrangement of the 

 more or less pronounced metamerism of that organ. Between 

 the intestine and the genital masses there is in some forms a 

 distinct cavity, or coaloinic space, and at the time of maturity 

 a separate communication with the exterior forms for each 

 ovary or testis. 



The class Nemertina may be divided into four orders, 

 whose chief characteristics may be briefly stated, having been 

 for the most part already described. 



1. Order Palseonemertini. 



To this order belong the genus Carinella and allied forms, 

 all characterized by structural peculiarities which are to be 

 regarded as primitive. The lateral ciliated organs are, as in 

 the Khabclocoela, mere grooves, not being continued inwards 

 to the brain in the form of a funnel ; and furthermore the 

 nervous system is either imbedded in the ectoderm or lies 

 immediately below it. To these characters may be added the 

 more or less lacuuar nature of the blood vascular system, and 

 the communication, in some cases, of the nephridia with it. 



2. Order Schizonemertini. 



In the Schizonernertmi the ciliated funnels are well devel- 

 oped, and the nervous system is imbedded in the muscular 

 layers of the body-wall ; and though the nerve-cords are still, 

 as in the preceding order, united by a plexus, nevertheless 

 there are indications of a development of coinmissural con- 

 necting nerves. The blood vascular system is still lacuuar 

 anteriorly, though posteriorly three well-defined vessels are 

 present. The genus Cerebratulus belongs here. 



