110 THE VOYAGE OF H.M.S. CHALLENGER. 
the first thoracic ganglion are very long, and through the wide canal formed by these 
not only the intestine passes but also two large muscles (Pl. XVIII. fig. 7), which serve 
for the movement of the proboscis, and run from the posterior margin of the proboscis to 
the hinder part of the dorsal surface of the cephalic part of the cephalothorax. These 
muscles are anteriorly narrow, and grow considerably broader towards their extremity, 
so that their shape is rather triangular. The nerves which arise from the supra- 
cesophageal ganglion are the same in Nymphon, Phowichilidiwm, and Colossendeis. To 
the front three comparatively strong nerves are always present.' Of these, that nerve 
which is placed in the middle takes its origin in the ventral surface of the ganglion, 
a little behind the front margin. This middle nerve is the azygous proboscideal nerve. 
It runs close to the dorsal surface of the proboscis, and gives off at rather irregular dis- 
tances extremely small nerves, which innervate the integument. At a distance of about 
one-fourth of the total length of the proboscis in Nymphon, and of about one-eighth of the 
same length in Colossendeis, it enters the ganglion (Pl. XVIII. fig. 8), which, no doubt, 
has already been observed by Dohrn. The two mandibular (antennary) nerves arise from 
the front margin of the supra-cesophageal ganglion ; they are nearly (in Nymphon and in 
Phoxichilidium) of the same strength as the azygous proboscideal nerve. First they are 
slightly divergent, then they approach each other again so as almost to touch the azygous 
proboscideal nerve, then they separate again and direct themselves forwards and a little 
upwards, running in the mandibles very close to that part of the dorsal surface which is 
nearest to the mandible of the other side (Pl. XVII. fig. 4, n.m.). In regard to the 
farther course of the mandibular nerve I could only observe that it divides into two 
branches. These nerves are not totally wanting in the genus Colossendeis, and con- 
sidering the case of Colossendeis gracilis with its distinct mandibles, we need not 
wonder at this. Yet the nerves are very short and represented only by rudimentary 
branches (Pl. XVIII. fig. 4, m). (Those of the interesting specimen of Colossendeis 
gracilis | was unable to observe without dissecting the specimen.) 
With regard to the innervation of thee yes, I observed distinct nerves arising from the 
supra-cesophageal ganglion. These I have described already in my paper on Pycnogonids, 
published in 1877, and their presence is confirmed by Dohrn’s observations. Dohrn (loc. 
cit., p. 37) says that they arise from the sides of the ganglion, and that they are widely 
separated from one another. Moreover, Dohrn tells us that there are two of them, and 
that they divide and innervate the eye in a peculiar way. I studied the innervation of 
the eyes in Nymphon brachyrhynchus, N. strémii, N. robustum, and in Colossendeis 
proboscidea. The latter species is a blind one ; its eyes are represented only by a small 
1 In the figure I give of the nerves arising from the supra-cesophageal ganglion of N. robustwm (Pl. XVII. fig. 4), 
besides these three nerves two thinner ones are figured, These, however, are not present, as I ascertained after the plate 
was printed off. Although I have given myself much trouble in trying to determine what it was I had mistaken for 
nerves, I have not succeeded. The thin threads have the appearance of narrow ducts; they extend backwards to 
behind the supracesophageal ganglion and pass between this ganglion and the upper surface of the cesophagus. 
