71 
lere is a veritable zone of 
lervous cells. This circum- 
)heral nervous system must 
)e of considerable importance. 
\t the margin there is also 
is usual a. great mass of 
:mbryonic cells, as the growth 
)f the body continues from 
lere. The differentiation of 
uch embryonic cells into 
nuscle cells and other body 
issue can here be studied. 
'he nerves of the dorsal side, 
Iso forming a network, have 
nuch smaller calibre than the 
Text-fig. 20. Emprosthopharynx opistho- 
porus. Ventrally situated nerve net at 
the side of the body, near the posterior 
end. ina, margin of the bodj'; pi, inter- 
spaces between the anastomosing nerves. 
It is perhaps superfluous to directly State that 
there is no discrete annular nerve along the body, 
(= „Ringnerv“) as in this respect text-figures 20 
and 22 are clear enough. Furthermore, a siudy 
of the sections support this statement. Lang 
mentions that on transverse sections of Ånonymus 
virilis Lang, he has obtained an impression of 
the occurrence of a „ringfbrmiger Randnerv“ and 
deplores the faet that he has not been able to 
decide it positively. He was aware of the occur¬ 
rence of such a nerve in the Triclads, and has 
consequently made his utmost to detect a corre- 
sponding nerve in the Polyclads, but with no 
success in other species. 
In the anastomosing network of the dorsal and 
ventral side, Emprosthopharynx shows the same 
general type as that found by me in other Polyclads. 
The stronger ventral nerve net in several Polyclads 
entral ones. 
