140 THE VOYAGE OF H.M.S. CHALLENGER. 
the same way, and (2) that here the word metamorphosis has quite a different meaning 
from what it has in entomology. 
Of the genus Nymphon I was able to compare the larve of the species Nymphon 
brevicollum, N. hamatum, and N. longicoxa. Of Nymphon brevicollum 1 have figured 
the youngest stage observed in figs. 12 and 13; an older one, which has three pairs of 
legs fully developed and the fourth already planned in the form of two lateral processes, 
has been drawn from the ventral side in fig. 1 of Plate XX. 
On the ovigerous legs of the same animal I found together larve in both the stages I 
have figured, and also in intermediate stages. Taking a small number of these larvee from 
the leg to study them under the microscope, I often observed the membranes of earlier stages 
between them. These membranes, and especially the parts which belong to the fore-part 
of the body, are attached to one another by means of long threads; these threads take 
their origin in the first joint of the foot-jaw, which bears a protuberance perforated by 
the thread. In the interior of the joint, and also of the empty membrane of this joint 
the thread can be traced a short way, but in neither to a great extent, as in the joint it 
is covered by the food-yolk, and in the membrane soon ceases after having passed the 
protuberance. 
The larvee of Nymphon hamatum which I was able to study were already furnished 
with four legs. Their condition was not extremely favourable for minute investigation, 
especially because the food-yolk makes the whole body opaque. The third pair of 
cephalic appendages are but small, and have each the form of a two-jointed stump bearing 
a pair of small spines at the extremity. The fore-part of the body of this larva is figured 
in fig. 3, Plate XX. An apparatus of a very singular shape, and, of course, closely connected 
with the protuberance perforated by the long thread in the larva of Nymphon brevicollum, 
is situated as in that species in the first joint of the foot-jaw. Numerous bottle-shaped 
sacs are placed near each other, and in such a way that their necks meet in one point. 
Each neck terminates in a small semilunar border, which covers a small slit; through 
this slit a thread passes, that can be easily observed as it runs through the throat of the 
bottle-shaped sac. The widened part of the bottle has in its interior two or more 
vesicles, which seem to be filled with an opaque protoplasm, covering in all probability 
the origin of the thread. Every bottle has its own thread, and of these more than ten 
are easily counted. I have figured this apparatus in fig. 4, Plate XX. The study of the 
apparatus is very difficult, as it is not transparent, being covered at one side by the food- 
yolk. The different bottle-shaped sacs are enclosed in a granular mass, with which 
very fine fibres seem to correspond. I could follow these fibres to a certain distance 
from the apparatus, where,they are covered by the food-yolk; and from their pale 
appearance, and the circumstance that they are not easily coloured by picrocarmine (as 
the muscles, fig. 4, are), I felt inclined to look upon them as nerve-fibres. 
The same organ, but of a somewhat different shape, occurs also in the mandibles of 
