RESEARCHES ON THE NERVOUS SYSTEM OF NEMERTINES. 277 
nervous apparatus, with respect to the muscular layers of the 
body wall on the one hand, and to the axis of the body on the 
other hand, seems, indeed, to justify the author’s conclusion 
that the Nemertines represent an ancient and primitive stock 
in which an apparatus, otherwise so stable as the central nerve 
chain, is subject to interesting variations, which point to 
higher stages of differentiation, apparently wide apart, 
which, however, are reached in other subdivisions of the 
animal kingdom. 
B. The side organs. — The curious apparatus, accessory to 
the Nemertean brain, which has been designated by so 
many diverse names (side organs, cephalic sacs, ciliated 
furrow, cephalic grooves, &c.), is here for the first time 
studied in the light of comparison. The author, who has 
had at his disposal all the different genera of European 
Nemerteans, has been able to study this apparatus in the 
most various stages, and develops his views as to its probable 
phylogenetic development, basing his views in the first 
place on the comparative anatomy, and secondly, on certain 
facts which recent embryological observations have brought 
to light. 
The lowest stage of differentiation of this apparatus is 
present in Carinella annulata (we leave Ceplialotlirix^ where 
it seems to be altogether absent, out of consideration), in 
which genus the epiderm shows a transverse, shallow fur- 
row, which is interrupted in the median line of the back, 
slightly bent, and situated about in a level with the middle 
of the brain. . This groove is ciliated. Series of transverse 
and horizontal sections showed no traces of any complica- 
tion of this arrangem.ent (PI. XXIII, fig. 2,). Where this 
furrow is situated, the distance separating the nerve- cells 
from the external ciliated surface of the body — a distance 
which all along the nerve-trunks is very insignificant indeed 
— is still more reduced, and the facility for osmotic inter- 
course augmented. 
Carinella inexpectata, a new species which the author has 
elsewhere described,^ agrees with Carinella annulata in all 
general respects. It differs from it in showing the apparatus 
just described more complicated by a few steps. Instead of 
the simple exterior transverse groove this species carries 
short parallel grooves placed perpendicular with respect to 
the one larger transverse one and confluent with it. In the 
middle of this transverse groove, strictly laterally, there is 
a small opening leading into a ciliated duct. This duct pene- 
trates the ectodermic tissues, and immediately enters amidst 
‘ ‘Notes from the Leyden Museum, vol. i, p. 93. 
