NOTKS OX THE 11 ISTIOOBDELLI D.T]. 
217 
and, in common with Shearer, I find my.self quite unable to 
come to a decision as to tlieir connections. 
Nervous System. 
The remarkable development of tlie nervous system in the 
Histriobdellida3, and especially in Stratiodrilns, dis- 
tinguishes them widely from any lowei* group with which we 
can compare them, and, if not constituting strong evidence of 
annulate affinities, is a very remarkable instance of convergent 
development. In Hist riobd el la this system was described 
with great thoroughness and completeness by Foettingei', and 
additional details were given by Shearer, and a careful com- 
parison with the nervous system of Dinophilus gyvo- 
ciliatus as described by Nelson ( 7 ). 
The nervous system of Stratiodrilns n o vjc-h ollan d i ae 
closely resembles that of S. tasmanicus. The cerebral 
ganglion (figs. 2 to 6, h.) contains a massive neuropile situated 
in the head towards the dorsal surface, somewhat in front of 
the middle of the region and well behind the mouth. In 
sagittal section this appears ellipsoidal in outline, with a 
slight dorsal depression indicating a division into anterior and 
posterior lobes. In horizontal section it is seen to be some- 
what more elongated transversely than antero-posteriorhq and 
to be divided by a wide posterior notch into two lateral lobes. 
Applied to the neuropile dorsally and laterally ai-e a great 
number of nerve-cells. These extend over the greater part 
of the head, and are continued backwards for some distance 
along the oesophageal connectives. This layer of nerve-cells 
is distinct from the epidermis, which is continued as a definite 
layer, with an occasional characteristic nucleus, between it and 
the surface. At the same time it lies distinctly outside the 
neuropile, and thus the appearance which the brain as a 
whole presents in sections is very characteristic, and differs 
in a very marked manner from the appeai-ance presented by 
-corresponding sections in the case of a Cha3topod. Probably 
in this, as in so many other points, there is a closer connection 
