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 (PI. XVIII. fig. 7), which serve 

 for the movement of the proboscis, and run from the posterior margin of the proboscis to 

 the hinder jiart 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 Ni/mplion, Phoxichilidium, 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 mai'gin. This middle nerve is the azygous proboscideal nerve. 

 It runs close to the dorsal surface of the prolioscis, 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 Nijmplwn, and of about one-eighth of the 

 same length in Colossendeis, it enters the ganglion (PI. XVIII. fig. 8), which, no doubt, 

 has already been observed l)y Dohrn. The two mandibular (antennary) nerves arise from 

 the front margin of the supra -oesojihageal ganglion ; they are nearly (in N[imphon and in 

 Phoxichilidmm) 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 Uttle 

 upwards, running in the mandibles very close to that part of the dorsal surface which is 

 nearest to the mandible of the other side (PI. XVII. fig. 4, n.m.). In regard to the 

 farther course of the mandibular nerve I could only observe that it divides into two 

 liranches. 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 (PI. XVIII. fig. 4, m). (Those of the interesting specimen of Colossendeis 

 gracilis I was unable to observe ■^nthout dissecting the specimen.) 



With regard to the innervation of the eyes, I observed distinct nerves arising from the 

 supra-oesophageal 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. stromii, N. robustum, and in Colossendeis 

 2')roboscidea. The latter species is a blind one ; its eyes are represented only by a small 



' In the figure I give of the nerves arising from the sxipra-cEsophageal ganglion of N. rohustum (PI. XVII. fig. 4), 

 liesides 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 supra-oesophageal ganglion and pass between this ganglion and the upper surface of the oesophagus. 



