118 THE VOYAGE OF H.M.S. CHALLENGER. 
distinct nerves are observed arising at an acute angle from the commissures. These 
innervate the muscles which run from the one segment to the following one. 
I give a figure (Plate XVIII. fig. 10) of one of the small ganglia and the nerve 
fibres arising from it on the inner surface of the integument, I observed these ganglia 
in Nymphon and in Colossendeis; they are more numerous in the latter genus, and 
especially numerous and in a better state of preservation in one of the specimens of 
Colossendeis proboscidea, Sab., dredged last summer north of Scotland. The figure is 
taken from a part of the integument of a specimen of this species. 
To show the minute structure of the ganglia I give in fig. 11 A—F a series of six figures 
illustrating vertical (frontal) sections through the supra-cesophageal and first thoracic 
ganglia. As will be easily seen, the sections do not form a complete series, they are only 
the most interesting out of a series of about twenty. Fig. A represents a section 
quite at the front of the supra-cesophageal ganglion ; a distinct and comparatively thick 
neurilemma sheath surrounds the whole ganglion, and three distinct medullary nuclei 
(pointed substance according to Leydig) show the place of origin of the three main 
nerves. The rest of the section is composed of ganglion cells, with the exception of a 
small medullary spot at the left side, which does not occur at the other side, 
and proves that the section is somewhat oblique. Neither the cesophageal com- 
missures nor the first thoracic ganglion are yet to be seen in this section, Fig. 
B represents a section which passes through the supra-cesophageal ganglion and 
through the foremost part of the first thoracic ganglion, but not yet through the 
commissures. Almost the whole section is occupied by the medulla, which forms 
regular prominences towards the periphery, and only a very small space is occupied by 
the ganglion cells; m is the lobe for the mandibular (antennary) nerve, 0 represents the 
lobe for the optic nerve, and z is a median lobe about the function of which I do not feel 
quite sure. In section C this median lobe is no longer to be observed, and the optic 
lobes have here assumed a much more elongated form. In section B the commissures 
are still totally wanting, but the front part of the first thoracic ganglion, with the 
medullary nuclei (p) for the two infra-proboscideal nerves, are distinct. These in 
section C are reduced to small lobes, while those for the nerves of the ovigerous legs (¢) 
are distinct. In this section the cesophageal commissures are seen, and also the under- 
most parts of the two optic nerves, which arise from the supra-cesophageal ganglion 
(o’). Their connection with the optic lobes, however, does not occur in this section. 
Section C passes almost through the middle of the oculiferous tubercle, so that two eyes 
are placed in front of this section and the two others behind it. Section D represents the 
last part of the supra-cesophageal ganglion ; the hindmost part of the medulla is seen, and 
the ganglion cells begin again to increase in number. Of the first thoracic ganglion, the 
section goes through that part of the medullary centrum which gives off the nerves for 
the ovigerous legs (7). In E this medullary centrum is considerably less voluminous, and, 
