REPORT ON THE PYCNOGONIDA. 139 
brachyrhynchus nor N. brevicollum nor N. hamatum agree with N. brevicaudatum 
in this regard. Fig. 8 shows a stage in the development of Nymphon brachyrhynchus, 
in which the three first pairs of embryonic appendages are already present. The first 
pair (the largest) are armed with pincers; the second and third are small, armed with 
curved hooks and not taking parts of the food-yolk ; of the true legs in this stage nothing 
as yet is to be seen. In figs. 12 and 13 I have figured a larva of Nymphon brevicollum 
showing the three cephalic appendages, the first pair of true legs almost completely 
developed, the second pair much shorter than the first, and not yet furnished with claws, 
the third only as a rudimentary process ; the fourth pair is totally wanting in this stage. 
Consequently I believe it is the rule in Nymphon, that the three pair of cephalic 
appendages are developed first of all, the legs appearing afterwards in regular succession. 
To return to Nymphon brevicaudatum, Miers, in figs. 9 and 10, I have figured embryos 
within the shell of the egg almost of the same stage ; with this difference only, that in 
fig. 10 the egg is figured as seen from the ventral surface. In fig. 9 also, a part 
of the dorsal surface being bent over to the ventral side has been drawn. In this 
last figure it is clearly shown that the dorsal surface of the embryo is at least at the 
anterior side lined with a shell-like thickening, the proboscis and the first pair of cephalic 
appendages being at their origin covered by this thickening as by a cap. Near the 
anterior side of this cap the double supra-cesophageal ganglion is situated, making it 
evident that in the border of this cap the anterior margin of the cephalic part of the 
embryo is to be seen; the proboscis being only an azygous excrescence of that part of 
the ventral surface which surrounds the mouth. 
The equatorial section figured in fig. 11 shows the distribution of the nerve ganglia 
on the ventral surface ; the first and second ganglia are smaller and are placed close to 
each other ; the development of the third, fourth, and fifth ganglia is in near relation with 
that of the corresponding legs; finally, neither the sixth ganglion nor the fourth pair of 
legs is to be distinguished, In the middle the two halves of every ganglion are placed 
close to each other, which, as far as I could ascertain, is also the case in earlier stages, 
Of the longitudinal commissures between the ganglia in this stage, nothing as yet is to be 
distinguished, and as to the cellular structure of the ganglia, I was only able to trace 
large cells without any differentiation. 
The degree of development the larvee have reached when leaving the shell of the egg 
is not the same for all the species of Nymphon ; so I think it probable that the larva of 
Nymphon brevicaudatum, Miers, does not creep out of the egg before the four true legs 
are developed, whereas the young of Nymphon brevicollum cling to the ovigerous legs 
of the father as soon as only one of the pairs of true legs has reached its full development, 
and perhaps even earlier yet. So, when Semper affirms that there occurs a complete 
metamorphosis in the development of the species of the genus Nymphon, two points 
are to be borne in mind, (1) that this does not affect all the species of Nymphon in 
