EEPOET ON THE PYCNOGONIDA. 101 



means of very narrow canals with the exterior, and that they occur in all the genera of 

 Pycnogonids (at least in those I had then studied — Nijmiyhon, Pallene, Phoxichilidium , 

 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 Nymplwn hamatum, N. longicoxa, N. brachyrhynchns, 

 and iV". hrevicaudatimi ; in Colossendeis leptorkynchus, C. gigcis, and C. 2^'>'oboscidea ; 

 in Ascorhynchus glaber and A. orthorhynchus ; in Pallene australiensis ; and in Phoxi- 

 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^ (PI. 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 lam i use ; 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, PI. XVI. fig. 9) or two {Nymp)hon hamatum, Phoxichilidium 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 PI. XVI. The septa of connective tissue, which in most genera divide the 

 cavity of the joints of the leg {Colossendeis, e.g., fig. 16, PI. XVI.), often have a point 

 of attachment in these ridges. 



As a rule the chitinous cuticle of the Pycnogonids 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 cylindricaUy shaped, is filled 



' The subcuticular epithelium of Pallene australiensis, Hoek, is richlj- furnished with a dark brown pigment. I 

 did not observe this in any of the other species. 



