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 Nymjyhon I was able to compare the larvas of the species Nymjihon 

 hrevicollum,, N. hamatum, and N. longicoxa. Of Nymiyhon hrevicollum I 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 larvae in both the stages I 

 have figured, and also in intermediate stages. Taking a small number of these larv« 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 larvae of Nymplion hamatum which I was able to study were already furnished 

 with four legs. Their condition was not extremely favourable for minute investigation, 

 esj^ecially 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 Nymplion hrevicollum, 

 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 ; tlu'ough 

 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 difiiciilt, as it is not transparent, being covered at one side by the food- 

 yolk. The diff'erent 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 difierent shape, occurs also in the mandibles of 



