DEVELOPMENT OF EUPHAUSIA SUPERB A 33 



They indicate also that there is more than one Cyrtopia stage, and remark that before the 

 adult stage is reached a large number of ecdyses must take place. 



Lebour (1926 c) in a paper entitled "A general survey of larval euphausiids, with a 

 scheme for their identification", recognizes a succession of Furcilia forms commencing 

 with that in which no pleopods are present and followed by others during which the 

 pleopods develop successively until all are setose and biramous. It is stated in this paper 

 that "the pleopods develop in different ways in several different genera, of which the 

 first three or four (forms) are the same and the last two or three are the same, but in be- 

 tween there are different orders of development some of which appear to be character- 

 istic of certain genera". In Thysanoessa, for instance, all five pleopods are simple buds 

 before any are setose. In Euphausia krohnii the first is setose whilst four are simple. 

 The commonest group found, it is stated, is one which occurs in five genera — Nycti- 

 phanes, Meganyctiphanes, Thysanopoda, Euphausia, and Nematoscelis — in which the first 

 pleopod is setose with the three following simple and the last not yet formed. In all the 

 genera with the exception of Euphausia the second pleopod becomes setose before the 

 last bud appears. Finally in Stylocheiron the first pleopod is setose with only two buds 

 behind. This paper later states that the distinctive stages nearly always seem to occur as 

 though certain stages were dominant. Thus in Stylocheiron it is Furcilia 7, that is, 

 according to the pleopod development, a form having three pairs of pleopods one pair 

 of which is setose. In Thysanoessa it is Furcilia 6, that is, a form having five pairs of 

 non-setose pleopods. In Euphausia krohnii it is Furcilia 9, a form in which the pleopod 

 arrangement is one pair setose and four pairs simple. Lebour's paper draws attention 

 to the jumping of stages in some species; it is stated that " Mr Elmhirst and Mr Mac- 

 donald from Millport tell me that Meganyctiphanes may jump several stages but they 

 always jump into a stage known for that genus. Mr Elmhirst has provided me with some 

 notes on Meganyctiphanes (reared in aquaria) in which one jumped from one to three 

 pairs of simple pleopods and one which jumped from three pairs of simple pleopods to 

 three pairs setose and two pairs simple." 



Macdonald (1927 b, p. 785), in his paper on "Irregular development in the larval 

 history of Meganyctiphanes norvegica", states that the Furcilia is to be recognized by 

 having the eyes no longer covered by the carapace and by the appearance of the pleopods. 

 He distinguished eleven stages of Furcilia, certain of which tended to be dominant and 

 others to be suppressed. He also found that " those Furcilia stages which were observed 



