102 THE VOYAGE OF H.M.S. CHALLENGER. 
with a protoplasmic substance, often containing nuclei. No doubt it is the protoplasmic 
epithelium which fills these latter canals. A nerve passes through them, and terminates 
at the surface of the cuticle in what Dohrn (loc. cit., p. 38) calls a “ Borstenapparat.” 
Dohrn never observed a single seta’ at the end of these canals; but always two or more 
(sometimes even a rosette of eight or nine) together. This observation of Dohm’s 
seems to be most accurate ; as a rule I found the integument of the species of Nymphon 
furnished with forked sete (Pl. XVI. figs 1, 2, 4, 7), one of the sete being often split 
again (fig. 3); that of Pallene australiensis shows also forked sete; the integument of 
Ascorhynchus glaber is also furnished with double setz, which are here extremely small 
and rudimentary. One of the species of Phowichilidium (P. patagonicwm) shows a 
combination of four or five (Pl. XVI. fig. 17), while in another species (Phoxichilidium 
pilosum) two combined setze are always observed. 
In Colossendeis sete are totally wanting; and thus in this respect the genus 
Ascorhynchus, with its rudimentary sete, stands between Nymphon and Colossendeis. 
According to Dohrn,’ this pore-canal, which terminates in these forked sete, “ often” 
takes its origin from one of the integumentary cavities, which he saw filled up with glands. 
Dohrn therefore considers these sete as tactile organs, having probably the special 
function of causing on irritation, by reflex action, the secretion of a poisonous fluid by 
the glands, which are situated in the conical cavities of the integument. I think this 
a very ingenious supposition, but I wish to state in opposition to it, that according to 
what I have seen of the matter—(1) as a rule the cylindrical and narrow pore-canals do 
not originate in the conical cavities ; and (2) that the occurrence of the glands in the 
conical cavities is the exception, and that, as a rule, these cavities are empty or partly 
filled up with a protoplasmic substance, nuclei, blood-corpuscles, &c. In the different 
species of Nymphon it hardly ever happens that the pore-canal with the sete takes its 
origin in a conical cavity ; in the species of Phoxichilidiwm it does not seem to be so rare 
(Pl. XVI. fig. 17), even in these species, however, it is by no means the rule. 
With regard to the form of the conical cavities, in the first place it must be men- 
tioned, that they have a most regular conical shape in the different species of the 
genus Nymphon, and also in some species of Pallene. In Phowichilidium they are of a 
more elongated form, and often a small lateral branch passes from the main canal near 
the extremity (Pl. XVI. fig. 17, 6). The genus Colossendeis shows these cavities of a 
much more irregular shape. As a rule every cavity is bifid, and terminates in two 
narrow pore-canals (Pl. XVI. fig. 12, c). The cavities are usually almost quite filled 
up with protoplasmic substance. In this genus I once observed distinct cells, with large 
1 Huxley calls “seta” all the hair-like processes from the fine microscopic down to stout spines, which are found 
‘on the outer surface of the cuticle (Crayfish, London, 1880, p. 197). I use the word here, and on the following pages, 
ina much more restricted sense; having already used the words hairs and spines for the integumentary appen- 
dages, I call “ sete” those which I consider as being more particularly of a sensory nature. 
2 Loc. cit., p. 38. 
