Anatomy and Histology of Nemer tines. 407 



conclusions : — Tlie cerebral ganglia of Nemertines and 

 Annelids are homologous ; tiie ventral commissure of the 

 Nemertine brain corresponds to that which connects the two 

 halves ot" the Annelid brain ; the dorsal commissure of 

 Nemertines is a structure sui generis and has no homologue 

 in the case of the Annelids ; the oesophageal commissure of 

 the Annelids corresponds to the lateral nerves of Nemertines. 



The author draws the last inference from the fact that the 

 Nemertine brain, which arises as an ectodermal thickening on 

 each side of the proboscis-invagination, is prolonged poste- 

 riorly into the lateral cords. Nevertheless it is not proved 

 that this brain is exactly the homologue of that of the 

 Annelids, which always includes a portion of the larval apical 

 ])late ; whereas in the Filidiuni, on the contrary, the apical 

 plate is thrown off. In any case I am inclined to compare 

 the lateral cords of Nemertines with the ventral cord of the 

 Annelids (the arrangement of the nerves which pass off from 

 the cords makes the comparison justifiable), without further 

 discussing the question whether the Nemertine brain is to be 

 regarded merely as an expansion of the lateral cords, or as a 

 special formation in the same sense as the brain of the 

 Annelid. 



The grounds on which we might institute a comparison 

 with the central nervous system of Turbellarians appear to 

 me to be of so general a nature that they must recede into 

 the background when contrasted with the resemblances 

 between the Nemertine and the Annelid nervous systems. 



The eyes of Nemertines, on the other hand, may be shortly 

 characterized as Turbellarian eyes. 



An agreement in the mode of origin of the lateral organs 

 of Nemertines and the ciliated pits of certain Ehabdocoela 

 (Microstoma?) has already been pointed out by Dewoletzky *, 

 who was also successful in proving the occurrence of similar 

 structures in the case of the Annelids. To this end the author 

 instances Lov^n's larva which is provided with ciliated pits, 

 the larva of Sipu7iculus, and also Ctenodrilus^ in which 

 v. Kennel t found cephalic pits, corresponding as it were to 

 the lateral organs of Nemertines. The similarity between 

 the lateral organs of Nemertines and the ciliated organs of 

 the Capitellidffi has been demonstrated by Eisig also. 



I will not attempt to find the homologues of the second 

 pair of lateral organs of the species of Carinella in the 



• Dewoletzky, " Das Seitenorgan der Nemertinen," Arbeiten aus dem 

 zool. Inst, zu Wien, Bd. vii. 1880. 



t V. Kennel, " Ueber Ctenodrilus pnrdulis,'" Arbeiten aus dem zool. 

 Institut zu Wiirzburg, Bd. v. 1882. 



