112 THE VOYAGE OF H.M.S. CHALLENGER. 



While the eye of Colossendeis prohoscidea, Sab., must probably be considered as 

 the most primitive condition, that of Nymphon rohustum is undoubtedly a degenerated 

 form. In the innervation of the different stages of development of the eye of the 

 Pycnogonids I believe I have pointed out one common feature, viz., that the two 

 nei-ves arising from the supra-cesophageal ganglion may be only partly considered 

 as optic nerves, and that it is much more in accordance with the facts to call 

 them integumentary nerves, branches of which have assumed the function of optic 

 nerves. For the investigation of the development of the organs of sense and especially 

 of the eyes, I believe the study of the Pycnogonida will yield in future very interesting 

 results. 



The nunilxT of thoracic ganglia in Nymphon, Colossendeis, and PhoxicMlidium 

 pilosum is five. Those of Colossendeis (C. prohoscidea, Sab., s]3.) are figured in 

 Plate XVII. fig. 2 ; those of Nymphon rohustum, Bell, in fig. 3 on the same plate. 

 In these three species the first ganglion (better called the first ganglionic mass) is 

 separated from the second by two distinct commissures, and in Nymphon rohustum 

 and Fhoxichilidiurn pilosum even the outward form of the ganglion shows its complex 

 nature ; on a longitudinal section it is seen to be composed of two distinct ganglia. 

 This anterior ganglionic mass supplies the two ventral parts of the proboscis, the 

 palpi, and the ovigerous legs ; three pairs of strong nerves are given ofl' by the 

 ganglion, which, judging from its anatomical structure and from its development [vide 

 Dolirn, loG. cit., p. 34, and also in this report sxd) embryology, with PI. XIX. figs. 11 and 

 13) is composed of only two pairs of original ganglia.'' For a long time I was greatly 

 puzzled with this fact, until the study of the nervous system of Colossendeis dispelled 

 my doubts. 



In fig. 4 of Plate XVIII. I figure the suj)ra-oesophageal and first thoracic ganglia 

 of Colossendeis megalonyx. The latter gives ofi" the two nerves for the ovigerous legs 

 (o), the nerves for the palpi (pa), which in the same way as the nerves for the 

 legs immediately divide into two branches, and in the third place the two nerves for the 

 proboscis {t"). Moreover, a fourth nerve (t') is observed, which serves also for the 

 innervation of the proboscis, and the fibres of which arise from the same part of the 

 ganglion as those of the main proboscideal nerve. For a short way these fibres run 

 parallel with the fibres of the commissures, so that this first pair of proboscideal 

 nerves seems to arise from these commissures.^ These same nerves are also present in 



' On page 32 of the same paper, DdIiiti asserts that in the first thoracic ganglion tliree nuclei are present of the 

 well-known " tibrilliiren Punktmasse." This does not agree with what I have seen in the three genera I studied, nor 

 does it agree, I believe, with what Dohrn himself says on page 34. 



^ In fig. 2 on Plate XVII. the ventral part of the nervous system of Colossendeis prohoscidea, Sab., sp., is figured. 

 From the first thoracic ganglion arise the nerves for the ovigerous legs (n. o. I.), and a strong nerve (the palpus nerve) 

 dividing into two branches (?i. jn. and n. p.). The most anterior, and at the same time most dorsal, part of this ganglion, 

 from which arise the two pairs of proboscideal nerves, and the commissures, has not been figured, having been removed 

 during the preparation. 



