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REPORT ON THE PYCNOGONIDA. 101 
means of very narrow canals with the exterior, and that they occur in all the genera of 
Pyenogonids (at least in those I had then studied—Nymphon, Pallene, Phowichilidium, 
and Pycnogonum). Moreover, I pointed out that as no respiratory organs are 
present in the Pycnogonids, respiration must necessarily be integumentary ; it was my 
conviction in 1877, as it is still, after a minute investigation of the Challenger material, 
that the principal function of these canals is to serve for respiration. Contrary to 
this opinion, Dohrn asserts that the cavities, with the pore-canals, which he says, were 
rightly described by me, “zur Aufnahme von Hautdriisen dienen.” To settle this 
question I investigated the structure of the integument of many species belonging to 
different genera. I studied it in Nymphon hamatum, N. longicoxa, N. brachyrhynchus, 
and NV. brevicaudatum; in Colossendeis leptorhynchus, C. gegas, and C. proboscidea ; 
in Ascorhynchus glaber and A. orthorhynchus; in Pallene australiensis:; and in Phowi- 
chilidium patagonicum, P. pilosum, and P. insigne. 
Notwithstanding that my researches were especially directed to this point, I only 
once succeeded in observing the glands referred to by Dohrn, and although I grant it is 
possible that in some cases this may be owing to the condition of the animals, yet I feel 
sure that as a rule these glands are not present. 
A short description of the integument may find a place here. It always consists 
of a subcuticular layer (epithelium), and of the chitinous cuticle. The subcuticular 
epithelium is of a protoplasmic nature, with nuclei imbedded in it! (Pl. XVI. figs. 1 and 
17, f); the chitinous cuticle in the different species shows a very different thickness, 
and always presents a stratified appearance. It is never calcified, and, as a rule, is 
coloured yellow by picrocarmine. Often, however, it shows two distinct lamin; an 
internal very thick one, coloured violet by the picrocarmine, and consisting of numerous 
alternately lighter and darker strata, and a comparatively thin external one, which 
assumes a yellow colour when treated with picrocarmine (PI. XVI. fig. 1). To strengthen 
the often extremely long and slender joints of the legs (especially the thighs and the two 
tibial joints), the chitinous cuticle is often furnished internally with one (Ascorhynchus 
glaber, Pl. XVI. fig. 9) or two (Nymphon hamatum, Phowichilidium insigne) longitudinal 
ridges, which project into the interior of the leg. The form of these ridges on a transverse 
section is by no means always the same, as may be seen from the figures 6, 9, 11, 16, 17, 
and 18 on Pl. XVI. The septa of connective tissue, which in most genera divide the 
cavity of the jomts of the leg (Colossendeis, e.g., fig. 16, Pl. XVI.), often have a point 
of attachment in these ridges. 
As a rule the chitinous cuticle of the Pyenogonids is perforated by two kinds 
of cavities, the one of an irregular conical shape, terminating externally in a narrow 
pore-canal; the other much narrower, and rather more cylindrically shaped, is filled 
? The subcuticular epithelium of Pallene australiensis, Hoek, is richly furnished with a dark brown pigment. I 
did not observe this in any of the other species. 
