KEPOET ON THE TYCNOGONTDA. 139 



hracht/rhynchus nor N. brevicollitm nor N. hamatum agree with N. hrevicaudatum 

 in this regard. Fig. 8 shows a stage in the development of Nmnjjhon hrachyrhi/nchvs, 

 in which the three first pairs of embryonic appendages are akeady present. The first 

 pair (the largest) are armed Tvith 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 Nyniphon hrevicollum 

 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 Nyniphon, that the three pair of cephalic 

 appendages are developed first of all, the legs appearing afterwards in regular succession. 



To retui-n to Nymjjhon hrevicaudatum, 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 dra'WTi. 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-oesophageal 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. 1 1 shows the distribution of the nerve ganglia 

 on the ventral surface ; the first and second ganglia ate 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 difi'erentiation. 



The degree of development the larvae 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 

 Nymp)hon hrevicaudatum, Miers, does not creep out of the egg before the four true legs 

 are developed, whereas the young of Nymphon hrevicollum 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, (l) that this does not affect all the species of Nymp)hon in 



