Anatomy and Histology of Nemer tines. 395 



change, owing to the recognition of a metaraeric arrangement 

 in certain organs in the middle and posterior portion of the 

 body in some more highly organized Nemertines. 



To Hubrecht must be ascribed the honour of having 

 demonstrated the existence of septa in tlie region of the intes- 

 tinal ca?ca, instead of the uniform development of the gela- 

 tinous matrix, the parenchyma, in which all the organs are 

 imbedded. This indefatigable investigator of Nemertine 

 anatomy was likewise unremitting in his insistence on the 

 constant relations shown in the arrangement of intestinal 

 c£eca, septa, blood-vascular loops, and, lastly, even of the 

 proboscis-sheath. 



I'he immediate object of all this was finally to sever the 

 connexion between the Nemertines and the Turbellarians, 

 and to enrol them among the Annulata. According to the 

 old-established classification the Nemertines were completely 

 merged in the 'J\irbellarians, of which they were merely 

 recognized as suborders. 



Hubrecht, however, did not stop at this, but sought to 

 establish relations between Nemertines and Vertebrates. In 

 this direction I cannot follow him. Far-reaching specula- 

 tions are permissible and justifiable only after an exhaustive 

 gtudy of the embryology of the form in question ; and in this 

 respect my work is completely wanting. 



Yet it has seemed to me that it may be interesting to com- 

 pare the various systems of organs, as we have learnt to know 

 them in the forms we have examined, with those of the 

 Kemertine genera not treated of in these pages, casting at the 

 game time a passing glance in the direction of the Turbel- 

 larians and the Annelids. 



Kemertines one and all possess a ciliated ectoderm. This 

 either carries the whole of the gland-cells of the integument, 

 and in this case rests on an almost structureless layer of 

 connective-tissue, a so-called basement-membrane, or a portion 

 of the gland-cells sink into the connective tissue, and we get 

 a cutis, which is often rich in muscle-fibres. The first of 

 these conditions is met with in all forms having a stylet in 

 the proboscis, the Enopla, as also in Carinella, and, according 

 to Hubrecht, in Carinina^ Carinoma, and probably, too, in 

 Cephalothrix. We find that a double layer of gland-cells, 

 on the other hand, is characteristic of Eiqyolia, CerehratuluSj 

 and Langia ; but, from the works of M'lntosh and Hubrecht, 

 we may conclude that it is present in Valencinia, Li'neus, and 

 Borlasia also. 



The development of a cutis is manifestly followed by 

 highly important changes, as exemplified in the appearance 



