112 THE VOYAGE OF H.M.S. CHALLENGER. 
While the eye of Colossendeis proboscidea, Sab., must probably be considered as 
the most primitive condition, that of Nymphon robustum is undoubtedly a degenerated 
form. In the innervation of the different stages of development of the eye of the 
Pyenogonids I believe I have peinted out one common feature, viz., that the two 
nerves 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 number of thoracic ganglia in Nymphon, Colossendeis, and Phoxichilidium 
pilosum is five. Those of Colossendeis (C. proboscidea, Sab., sp.) are figured in 
Plate XVII. fig. 2; those of Nymphon robustum, 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 robustum 
and Phowichilidiwm 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 off by the 
ganglion, which, judging from its anatomical structure and from its development (vide 
Dohrn, loc. cit., p. 34, and also in this report swb embryology, with Pl. 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 supra-cesophageal and first thoracic ganglia 
of Colossendeis megalonyx. The latter gives off the two nerves for the ovigerous legs 
(0), the nerves for the palpi (pa), which in the same way as the nerves for the 
lees immediately divide into two branches, and in the third place the two nerves for the 
proboscis (¢’”). Moreover, a fourth nerve (¢’) 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 
1 On page 32 of the same paper, Dohrn asserts that in the first thoracic ganglion three nuclei are present of the 
well-known “fibrillaren 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. 
2 Tn fig. 2 on Plate XVII. the ventral part of the nervous system of Colossendeis proboscidea, 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 (n. pr. 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. 
