100 THE VOYAGE OF H.M.S. CHALLENGER. 
APPENDIX II. 
CONTRIBUTIONS TO THE ANATOMY AND EMBRYOLOGY OF THE 
PYCNOGONIDA. 
Our knowledge of the anatomy and embryology of the sea-spiders is very insufficient ; 
of those living in shallow water we know but little, and of the deep-sea forms nothing. 
Whereas a prior? it is evident, that in general the deep-sea animals will exhibit the same 
anatomical structure, and pass through the same development as the littoral or shallow- 
water forms; it is also clear, on the other hand, that a comparison of the anatomy of 
animals inhabiting very different depths might lead, at least in the case of some organs, 
to very interesting results. 
_ As the rich material collected during the voyage of H.M.S. Challenger enabled me to 
study the anatomy of at least some genera (Nymphon and Colossendeis), I eagerly made 
use of this opportunity ; in the first place, in the hope of increasing our knowledge of the 
morphological structure of the group, so that the question of their position in the zoological 
system might perhaps be settled; and in the second place, to try in this way to illus- 
trate the mode of life of those deep-sea animals which belong to our group. 
My original intention of going through the whole anatomy of the Pyenogonids I have 
given up, seeing that, however good the condition of the material might be, yet in regard 
to some organs,— intestine, heart, &c.,—and for the histological structure of most organs, it 
by no means takes the place of fresh material. Moreover, as I learned after a great part 
of my anatomical researches was finished that Dr Dohrn’s Monograph is forthcoming, I 
determined to limit the publication of my researches to those organs which had suffered 
least from having been in alcohol for so many years. These are the integument, with 
its glands; the nervous system, with the sensory organs; and the reproductive organs. 
In regard to the intestine, the heart, &c., only some incidental observations were made, 
which, in so far as they are thought important enough, will be recorded also. 
1. Integument.—The integument of the Pyenogonids is only known from the publica- 
tions of Zenker (1855),’ myself (1877),? and Dohrn (1879).? Zenker was the first to 
observe the numerous cavities in the chitinous cuticle of Pycnogonum litorale. I, 
however, had the good fortune to demonstrate that these cavities communicated by 
1 Zenker.—Untersuchungen tiber die Pyenogoniden, Miiller’s Archiv, 1852. 
2 Hoek.—Ueber Pycnogoniden, Niederlindisches Archiv fiir Zoologie, iii., 1877. 
3 Dohrn.—Neue Untersuchungen tiber Pycnogoniden, Mitth. Zool. Stat. Neapel., i., 1879. 
