PR1APULUS AND HALICRYPTUS. 
211 
ment in the posterior part of the ganglion. A little more 
towards the anterior end nerve-fibres make their appearance in 
the centre between the small cells and gradually displace the 
cellular part, until they occupy the position which I have 
described in dealing with the arrangement in the body proper. 
In his anatomy of Halicryptus, Saenger describes lateral 
nerves going off from the main trunk and surrounding the 
body in a similar way as in Sipunculus nudus. The median 
fibrous mass, he says, remains without a change at the points 
where the branches originate, and does not send any fibres 
into them. In spite of my endeavours to find these lateral 
nerves, I have not been able to identify them. Horst did not 
find them either. On the other hand, Daniellsen and Koren 1 
mention that the central nervous cord sent off numerous 
branches to the skin and muscles. 
In Echiurus Pallasii 2 the cellular portion runs along the 
whole of the cord in its peripheral part. A canal situated 
immediately under the dorsal median line is mentioned in 
GreefFs 3 description of Echiurus, who supposes it to be a 
remainder of the invagination from the Ectoderm. According 
to Andreae 4 the arrangement in Sipunculus nudus is rather 
different. The cord also lies internally to the muscular system, 
and consists of a sheath of connective tissue forming an 
external neurilemma. The nervous elements are surrounded 
by a similar internal sheath, and between the two lies a finely- 
granulated mass with small nuclei but without cells. 
It will be seen by the above description that I have not 
been able to trace any peripheral nerves coming off from the 
nerve-cord. It would be rash to assert on the strength of 
this that they do not exist, and a further examination of fresh 
specimens is needed to clear up these doubts. At the same 
time I think it quite possible that the whole of the hypodermis 
acts as a kind of nervous layer. On the other hand, the well- 
1 Daniellsen and Koren, loc. cit., p. 17. 
s Spengel, loc. cit., pp.484 — 86 . 
3 Greeff, loc. cit., p. 85. 
4 Loc. cit., p. 249. 
