142 THE VOYAGE OF H.M.S. CHALLENGER. 
branchiata. The larvee of different species, as observed by me, usually remain for a 
long time after having cast off their exuvie, in relation to the ovigerous leg of their 
parent. As long as they were enclosed in their egg, they clung together tightly enough ; 
but once crept out of the egg-shell, a special arrangement is necessary to keep them 
together. This is found in the threads, and the supposed glands from which these take 
their origin, as observed by Dohrn and me. Repeatedly I saw, as I have mentioned 
already before, between the larvee of Mymphon brevicollum, collections of very numerous 
skins held together by means of the threads, and small parts of such a cast skin I found 
also in relation with the thread of the larvee of Nymphon longicoxa. 
It is true that the structure of the apparatus, as it shows itself in the larva of Nym- 
phon hamatum, argues, perhaps, for the conjecture that the organ is an organ of sense, 
but then it is exceedingly strange that such an organ should only be found within the 
larvee. And it would be difficult to explain the meaning of the single or numerous long 
threads as being sent forth from an organ of sense, whereas in relation with a gland their 
function can easily be understood. 
The study of this same organ which I made last summer in the laboratory of Prof. 
Lacaze-Duthiers, at Roscoff, has also convinced me, that my original supposition as to the 
function of these organs was erroneous. The fine threads, which I observed in the 
interior of the mandible running towards the organ are threads of connective tissue ; 
their function is, no doubt, to hold the organ in its place. The young of Nymphon 
robustum, Bell, and those of Nymphon brevicaudatum, Miers, are a great deal more 
developed when creeping out of the egg than those of Nymphon hamatum, N. longicoxa, and 
N. brevicollum. Most probably this spinneret of the larva does not occur in these species. 
Besides the larvee of the genus Nymphon, the only other genus of which I could 
investigate the larvee was Ascorhynchus. About their development and metamorphosis 
nothing as yet has been published. I can only give a drawing of the single larval 
stage which I observed, and which is furnished with three pairs of legs. The fig. 6 
on Plate XX. shows that the larva in this stage corresponds with larvee of other genera, 
as observed by Kroyer, Dohrn, and myself. Of the glands in the foot-jaw no trace 
could be discovered; but then the larvee are very small, and their condition is not very good. 
8. In studying the anatomy of the Pyenogonids of the Challenger Expedition, I met 
with two different kinds of bodies of which I have not been able to ascertain whether they 
really belong to the organisation of the Pycnogonids, or must be considered as parasites. 
However, I feel much inclined to adopt the latter opinion; and although some doubt 
remains, I wish to give a short description of what I have seen, which may, perhaps, 
be of use for later investigators. 
In the first place I met with some curiously shaped forms in the interior of the body and 
of the legs of two different species of Nymphon. I observed them in Nymphon longicoxa 
and in Nymphon brevicaudatum, but only in some of the specimens which belonged to 
