406 
Dr. O. Burger on the 
of the body-wall we have the lateral indentations known as 
cephalic pits in the majority of the representatives of Group II. ; 
these supply the place of a canal in bringing the lateral organs 
into communication with the outer world. We have yet to 
mention the existence of a pair of lateral organs in the neigh- 
bourhood of the nephridio-pores of Carinella . 
While the Nemertines, owing to their plexus-like epithelial 
and subepithelial nervous layers, give grounds even for a 
reference to the Coelenterates (a vista opened up by Hubrecht) , 
nevertheless the central nervous system shows so high a 
degree of development, in the stoutness of its central sub- 
stance, of its ganglionic coat (so widely and so sharply 
differentiated from it), and of the twofold membranous and 
fibrillar elements of its sheath, that it equals the Annelids in 
this respect. The appearance of a second sheath surrounding 
the central substance is of especial importance. An inner 
neurilemma of this kind, which interposes itself between the 
coat of ganglion-cells and the fibrillar substance, has been 
identified and described by Hermann * in Hirudo also. The 
tissue, however, which has been styled by many authors an 
inner neurilemma, does not correspond to the inner neuri- 
lemma of Nemertines. For the term has been applied to the 
finely fibrillar elements of the sheath of the ganglion-cells 
(Nansen t)> or to a membranous sheath which surrounds the 
nervous elements, ganglion-cells, and central substance of the 
ventral cord of certain Annelids, and which, as an inner neuri- 
lemma, has been contrasted with an outer one, which envelops 
an intei mediate mass lying between the two membranes 
(Ley dig Andrew §). 
In other respects the connexions which can be made out 
between the brain of Nemertines and that of Annelids are 
many in number. I may instance in particular the fact which 
has lately been more and more insisted upon, viz. that the 
ganglionic coat consists almost exclusively of unipolar 
ganglion-cells, and lastly, but by no means least, the occur- 
rence in Nemertines also of neurochord-cells and neurochords. 
Whether we are justified in placing the brain of Nemer- 
tines absolutely on a level with that of Annelids appears to 
me to be a question which must be postponed for the present 
on embryological grounds. Salensky arrives at the following 
* Hermann, 1 Das Centralnervensystem von Hirudo medicinalis ' 
Munch en, 1875. 
t Nansen, 44 Anatomie u. Histologie des Nervensystems der Myzo- 
stornen/’ Jenaische Zeitschr. 1887. 
X F. Ley dig, 4 Tafeln zur vergl. Anatomie/ Tubingen, 1864, i. fig. 9. 
§ J. Andrea), 44 Beitrage zur Anatomie und Histologie des Sipunculus 
nudus ” Zeitschr. fiir wise. Zuologie, Ed. xxxvi. 
