PYCNOGONIDA. 25 
embryonal legs, or, at all events, of their exoskeleton is accordingly out of the question, we must sup- 
pose them to be thrown off at once. 
In his first essay, «Om Pycnogonidernes Forvandling» (On the metamorphosis of the Pycnogo- 
nida) 1840, Krøyer already gives a rather detailed description of this stage, but of the embryonal legs 
he has only seen one pair;' his words are (1. c. p. 303): «Between the chelifori and the first pair of feet 
I have sometimes seen projecting on the side a little process, fig. 3 c, appearing to consist of only 
two joints and of a length of abt. /,.'” (Danish); after its position I think it must be taken to be the 
first trace of the palps.» The interpretation by Krøyer of this «little organ», to be sure, was not 
correct; but to this question I shall recur in the following, in the section on the Psewdopallene-larva; 
here I shall only add that the figure of the larva itself, fig. 34, is bad, and consequently the repro- 
duction of this figure and other ones from his plate III, as they are given after the drawings 
by Thornam, in the work of travel of Gaimard (1849) pl. 39, fig. 1 a—2, must be considered as a great 
progress. In the work of travel the new principal figure, fig. 1 d, resembles very well our fig. 23, and 
the pointed thorns or hooks with which also the limbs behind the chelifori here are seen to end, agree 
very well with the outermost joint or hook of the embryonal legs, but not with the imaginal fore 
limbs in any stage whatever. 
The second species the development of which I have been able to follow, is Nymphon robustum, 
and I shall here describe the second stage, referring to my figures, pl. II, fig. 2—6. A peculiarity of 
this species, when compared with most of the other species, is the long time, during which the larva 
remains confined in the egg-shell, or the egg-membrane and cast-off larval sloughs"). The first stage 
of the larva in my possession is the second stage, shown in fig. 2: here the larva is seen enclosed behind 
by two membranes besides the egg-shell, and that it is not only the trunk which has cast off its 
slough, may be seen from the proboscis, of which one cast-off slough is seen enclosed in the other, as 
I have shown it more distinctly by a special figure, fig. 3. In fig. 2 otherwise, all four pairs of ambu- 
latory legs are seen in a course of development, the first pair as usual farther proceeded than the 
others, but still only with slight constrictions indicating the beginning articulation. The segmentation 
of the trunk is already here discernible, and it may also be observed that the first pair of embryonal 
legs more than usually are distinguished by being earlier developed and thicker than the segeond pair; 
as it is the case with the first pair of ambulatory legs, the old slough is also here seen loosely wrapping 
the first pair of embryonal legs. In fig.4 showing a stage a little more advanced, the proboscis as 
well as the abdomen is seen lying in the two last sloughs; the second pair of ambulatory legs have 
hére grown comparatively more than any of the other limbs; besides the byssus-threads are now 
secerned. In fig. 5 and 6 the development has proceeded still farther, the two foremost pairs of am- 
bulatory legs are completely articulated, while the third pair is still much shorter than the others, 
and the articulation not quite finished. In fig. 6 showing the larva from the lower side, the byssus- 
gland is developed. The auxiliary claws are as a rule very small though quite distinct, which feature 
is characteristic of the species. 
Of Nymphon macronyx 1 possess, besides the larva on the first stage mentioned in the fore- 
1) It is also this species that for a longer time than any other Pycnogonid clings to the ovigerous legs of the father; 
comp. the representation of this fact by Hoek, Pycnog. «Willem Barents», 1881, Taf. II, fig. 35. 
The Ingolf-Expedition. IL r. 4 
