DEVELOPMENT OF EUPHAUSIA SUPERB A 37 



minally on the telson, but it is the earlier Furcilia forms up to the point where five pairs 

 of pleopods, all setose, are found which are to be discussed here. Within these limits 

 thirteen different kinds of Furcilia occur. As in the frequency expressed by the number 

 of stations at which they were present, so here, by the frequency of individuals, two 

 maxima are recognizable: (i) larvae having four or five pairs of non-setose pleopods, 

 and (2) larvae having either four pairs setose and one pair non-setose, or all five pairs 

 setose. These are represented in far greater abundance than other combinations of 

 setose and non-setose pleopods and are the dominant stages. 



Table XI. Euphausia superba larvae from St. WS 527 



* In this sample only a quarter of the total was analysed. 



Inspection of the varying forms of pleopod found amongst the Furcilia at this station 

 shows that without retrogression in development, either in the number of pleopods or 

 in the formation of setae, the larvae cannot moult successively into all the different forms 

 found. Thus those with four or five pairs of non-setose pleopods cannot moult into forms 

 having three pairs of pleopods, two pairs of which are setose and one pair non-setose, 

 without diminishing the number of pleopods. Or if this three-pleopod form be con- 

 sidered less advanced than that having four or five pairs of non-setose pleopods, it can- 

 not moult into one of these latter forms without losing the setae on the first two pairs of 

 pleopods. For the same reasons larvae having two pairs of setose and one pair of non- 

 setose pleopods cannot follow or be followed by forms having one pair setose and three 

 pairs non-setose, nor can larvae having four pleopods, all setose, follow or be followed 

 by forms having five pleopods, three pairs of which are setose and two non-setose. 



