On the Development of some Pelaijlc Decapods. 163 



the pelagic Crustacea, has described *, uuder the name of Elujjho- 

 caris, a small and very spiny Zoea caught in the harbour of Messina. 

 He calls it the larva of a Decapod without fixing its position. 

 This small larva was often seen by me m the Atlantic ; but I only 

 lately found out that Elajphocaris is the larva of a species, or rather 

 of some species, of Sergestes. There is, however, one species of this 

 genus in which the Zoea is not an Elaphocaris, but a larger, less 

 spiny form, similar, however, in all other respects to the former. 

 Of the species which de^'elops with an Elaphocaris-sta,oQ in the 

 Western Pacific, I ha\'e collected numerous specimens of all the 

 stages, from the youngest Zoeas up to the mature animal. The 

 mode of development is very simple. After the first moulting the 

 larva gets sLx more branched legs and loses many spines. It 

 enters the ^mj>/«'on-stage, then moults, throws the branched legs 

 off, gets branchijB, and becomes a young 8er<jestes. Only after this 

 last moulting the central eye, hitherto present, disappears. 



And very similar to that of Sercjestes is. the development of 

 Leucifer. Here the earliest Zoea of a species from the Western 

 Pacific has got at first no eyes, then sessile ones come out, and 

 the animal then presents the form which Dana has called Erich- 

 thina demissa, and which Claus suspected to be not a Stomatopod 

 but a Schizopod lana. After the second moulting this Erichthina 

 gets stalked eyes and very long setae on all its appendages, becoming 

 a rather long, very delicate Zoea. It now enters the Amphion- 

 stage, but never gets more than four pairs of pereiopods, and loses 

 another pair of these when it moults for the yoimgest Leucifer- 

 stage, in which two pairs of pereiopods are r.bsent. 



The next question, after having found this out, was, of course, 

 whether Amphion, Sergestes, and Leucifer lea^e the egg as a Zoea, 

 or whether there is a preceding Nau])lius-s>'i:iige. My own impres- 

 sion is that in the two first-named genera this is not the case, as 

 the youngest Zoeas which I caught had all the same size, and as 

 none of them was without the large lateral stalked eyes. As 

 for Leucifer, the question appears to me to be doubtful ; for it 

 is, from what I have seen, quite possible that my youngest Zoea, 

 which has only got a central eye, may be preceded by a Nauplius. 

 Of course the simplest thing would be to get the eggs ; but there 

 is the difficulty, for Ampliion is caught very rarely, and has never 

 been obtained at any other time but between 8 and 12 p.m., when 

 it is extremely difficult by lamplight to find out the youngest stages. 

 Serffestes larvie are commoner, appearing also in the daytime, and 

 Leucifer is sometimes caught in abundance. I hope, therefore, 

 that I shall succeed in completing my researches about this ques- 

 tion, especially as far as the latter two genera are concerned. 



H.M.S. ' Challenger,' Ilonohilu, Sandwich Islands, 

 July 30, 1875. 



* V. Sieb<jkl mid Kollikcr, Zeitsclirii't i'lir wissenschnrtUche Zoologic, iJand 

 XX. p. 062, tab. 31. fig. 1'8. 



