PERIPHERAL NERVOUS SYSTEM IN NEMERTINES. 441 
This sensitiveness, with which the Schizonemertini are 
none the less endowed than the Hoplonemertini, would 
appear the more remarkable in the former in the absence of 
peripheral branches springing from the longitudinal marrow- 
trunks. The presence, however, of a sheath of nervous 
tissue in every region of the body, either immediately under 
the epiderm or inside the muscles, and sending out processes 
as well to the exterior surface as to the internal muscular 
layers, is quite as sufficient an explanation for this 
extreme sensitiveness as we before showed it to be for the 
persistence of life in the several fragments, which even de- 
veloped normal spermatozoa months after they had become 
separated. 
x\s will be understood from the contents of the foregoing 
pages, my investigations into this curious distribution of 
nervous tissue in the body- wall of the Nemer tines are far 
from being either complete or exhaustive. Not having as 
yet had occasion to examine fresh specimens with special 
regard to this nervous layer, I must reserve the more delicate 
histological questions for a future publication. The direct 
connection between the fibrillar plexus and the exterior 
cellular layer of the body, the presence of any distinct 
sensory cells in this ectodermic layer, as well as the connec- 
tion wdth the muscular fibres, on the other hand — all this can 
only be studied in careful preparations, teased out from the 
tissues when quite fresh, according to the delicate methods 
which have, for example, been so successfully applied by 
0. and R, Hertwig, in their splendid researches upon the 
nervous system of the Coelenterata (‘Das Nervensystem und 
die Sinnesorgane der Medusen,' and further ‘Die Actinien, 
anatomisch-histologisch mit besonderer Beriicksichtigung 
des Neuromuskelsystems,’ 1878-80). 
Having as yet only had series of sections mounted in 
balsam at my disposal, I could not expect to penetrate into 
all these histological details merely by their aid ; and if, 
nevertlieless, I venture to publish these preliminary re- 
sults it is because they appear to me to possess an increased 
interest now that the researches above mentioned ’ of 
O. and R. Hertwig have come before the public. The very 
lowest stage of differentiation in which nervous tissue is at 
present known in the animal kingdom was found by these 
searchers! in the Actinia, wffiere it appears as a fibrillar 
plexus, with nerve-cells indiscriminately scattered in it 
* Might not this word take the place of the barbarous savants^" so 
often met with in English scientific papers of the present day 'r* It would 
correspond to the German “ Forscher.” 
