170 THE VOYAGE OF H.M.S. CHALLENGER. 



series along the aliruptly tnincatc middle pnrt, wliercas the six others are arranged, three 

 on eitlier side, along the obliquely rounded lateral corners. Of the latter, the innermost 

 is by far the largest. In the later stage, the telson has become considerably narrower, 

 and the middle part of the apex (fig. 28) has begun to jut forth as a still rather broad 

 projection, truncate at the tip. 



Cyrtopia Stage (figs. 2.5, 29). — The transformation of the antennae clearly distinguishes 

 this stage from the two former as a true Cyrtopia. The animal has now attained a 

 length of 4-| mm., and may easily be recognised as a young Nematoscelis rostrata. The 

 first pair of legs are considerably elongated and slender, having nearly attained the 

 structure characteristic of the adult animal, and the gills are also more fully developed. 

 All the pleopoda have assumed their definitive form, and the luminous apparatus would 

 also seem to be distinctly developed. The telson closely resembles in form that of the 

 adult animal, but still retains some of the larval sj^ines. The middle projection of its 

 extremity (fig. 29) is considerably produced, but narrowly truncate at the tip ; and of 

 the seven original spines, three only remain. Of the three outer spines, the innermost 

 on either side is much larger than the others, and has assumed the character of the 

 subapical spines. In a succeeding stage, the outermost on either side is withdrawn to 

 the dorsal face of the telson, thus constituting the posterior pair of the dorsal denticles 

 of the adult animal, whereas the intermediate spine has altogether disappeared. 



Larval Stage of Eup)hausia sji. (?). 



First Furcilia Stage (PI. XXXI. figs. 30, 31). — I give a figure of this larva, not only 

 because it exhibits an unusual size and a rather peculiar aspect, but also because another 

 stage of precisely the same form has been described at a much earlier date, without, 

 however, having been at that time recognised as a larva of Eiiphausia. 



In the second ])iwt of his researches on the structure and development of the 

 Arthropoda,^ Professor Dohrn has given figures and descriptions of several very remark- 

 able larval forms,^ of which that figured in plate 30, fig. 54 undoubtedly represents a 

 Calyptopis stage of precisely the same form as that treated of here. This larva was met 

 with in the Indian Ocean, and regarded by Professor Dohrn — though with some reservation 

 — as a Peueuszoea. That this assumption is erroneous, and that the larva in question 

 should be comprised under the Euphausiidse, I feel no doubt whatever in asserting ; and, 

 moreover, I think there are reasons for assuming both these larvje to belong to a large- 

 sized species of the genus Euphausia, perhaps that briefly mentioned by the late Dr. v. 



' Zeitschr.f. wiss. ZooL, Bd. xxi., p. 35G, 1871. 



* I take the present opportunity of stating my conviction that the forms described by the said author as Cerataspis 

 monstruosa, Gray, and Ceratcspis lonijircmis, n. sp., and considered as adult animals belonginf; to the Schizopod tribe, 

 are both of them larvaj in the last stage (Mysis stage) of some large forms of Macrura of the Homaroid group. 



