162 Royal Society : — 



" Prelimiuary Eemarks on the Development of some Pelagic 

 Decapods." By E. von "Willemoes-Suhm, Ph.D., Naturalist to 

 the ' Challenger ' Expedition. 



Since we left Australia I have investigated the metamorphoses of 

 some Crustacea which have been constantly caught by us on the 

 surface of the tropical and subtropical parts of the Pacific. 

 Though these investigations will be continued, I have now arrived 

 at certain results which I think will not be uninteresting to zoolo- 

 gists. The genera to which these remarks refer are Amphion., 

 Sergestes, and Leucifer. 



Amphion Reijiiaudi has been on our lists as an animal " incertce 

 sedis" (Milne-Edwards) for nearly forty years, until Dohm proved 

 that a full-grown specimen of it, which he dissected, was in pos- 

 session of branchiae and of an ovary, therefore no doubt a mature 

 form. He also described one of its young stages, which has the 

 number of appendages of a Zoea, but in which caudal appendages 

 are already developed. 



On our voyages in the ' Challenger ' we have caught several 

 specimens of Amphion and of its larvae ; and I am now able to 

 produce drawings, not only of the true Zoea with a simple telson, 

 but also of all the intermediate stages between it and the adult 

 form \\-ith two, three, four, five, and six pairs of walking-legs. 

 Of the full-grown Amphion I have examined three specimens, two 

 of which are undoubtedly males, as the testes (and the branchiae) 

 were plainly visible, the former opening into the last pair of 

 legs. 



There is now no doubt that Amphion is not a larva, nay, even 

 that there are several species and perhaps genera of this remark- 

 able form. We have caught two very interesting mature animals 

 which are certainly closely allied to Amphion. One of these has 

 enormously long eye-stalks, which, having a length of 7 millims., 

 are just as long as the whole animal's body. Another form has 

 got very long eye-stalks too, but is especially remarkable for the 

 antepenultimate joiuts of its pereiopods, being large paddle-shaped 

 organs, terminated by a A-ery small end-joint. Both have got, like 

 Amphion, a central (Xauplial) eye and eight pairs of branched 

 legs ; but their body is more Sergestes-Vike and less flat than that 

 of Amphion. They certainly both belong to the same genus, and 

 may be called Amphiones until more than one specimen of each has 

 been obtained. 



To me these Amphionidae are especially interesting, as I can 

 compare them with the larvae of Sergestes and Leucifer, the former 

 of which have also got eight pairs of branched legs and the cen- 

 tral eye which persists in the Amphionidae. There are good reasons 

 for the statement that the larvae of Leucifer and Sergestes pass 

 through an ^?n^:*7iio n-stage; and this, it seems to me, throws a good 

 deal of light on the relations and systematic position of Amphion 

 itself. 



Dohm, to whom we owe so many fine discoveries concerning 



