Anatomy and Histology of Nerner tines. 407 
conclusions : — The cerebral ganglia of Nemertines and 
Annelids are homologous ; the ventral commissure of the 
Nemertine brain corresponds to that which connects the two 
halves of 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 
plate ; whereas in the Pilidium , 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 Rhabdocoela 
(Microstomas) 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&i’s larva which is provided with ciliated pits, 
the larva of Sipunculus , and also Ctenodrilus , in which 
v. Kennel + 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 Capitellidae 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 Garinella in the 
* Dewoletzky, “ Das Seitenorgan der Nemertinen/’ Arbeiten aus dem 
zool. Inst, zu Wien, Bd. vii. 1886. 
t V. Kennel, 11 Ueber Ctenodrilus pardalis,” Arbeiten aus dem zool. 
Institut zu Wurzburg, Bd. v. 1882. 
