442 
DR. A. A. W. HUBRECHT. 
throughout a great part of the ecto- and entoderm. In the 
oral plate (Mundscheibe), where the nerve-cells are more 
numerous and situated closer to each other, there is a ten- 
dency towards a certain degree of centralisation. 
It cannot be denied that this primitive arrangement offers 
strong analogies to the nervous plexus above described for the 
Nemertines, which, on the other hand, approach, in the his- 
tology of their nervous system, in many respects to what 
A. Lang has so carefully described for other Platyelmi^jthes 
Untersuchungen zur vergleichenden Anatomie und Histolo- 
gie des Nervensystems der Plathelminthen.’ 1. Das Nerven- 
systems der marinen Dendrocoelen. 2. Das Nervensystem 
der Trematoden ; Mitth. aus der Zool. Station zu Neapel, 
1879-80). And so I thought that giving my results, even in 
their incomplete form, might be suggestive of further re- 
searches into these questions; the more so because, in a former 
paper Verhandelingen v. d. Kon. Akad. v. Wetensch. te 
Amsterdam,’ vol. xx, 1880 ; cf. July number of this Journal), 
I insisted upon the phylogenetic importance which the 
nervous system of the Nemerteans appears to possess when 
compared to that of the Anxulata, on the one hand, and 
of the Yertebrata, on the other. 
In the monograph on this group of worms, which I have 
now in preparation for Professor Dohrn’s series of publica- 
tions, illustrating the Fauna and Flora of the Bay of 
Naples, I hope to be able to' furnish evidence about 
those points in w^hich the present paper confesses to be 
deficient. 
