DEVELOPMENT OF EUPHAUSIA SUPERB A 51 



in the larval history. It is merely one of several changes in form, and presumably in 

 function, which take place in the larval appendages in the process of development. 

 These changes are probably intimately connected with the provision of other appen- 

 dages to do the work performed in earlier stages of the life history by those more 

 anteriorly placed. 



The name Furcilia will therefore be used here to describe all the later developmental 

 stages in Eiiphansia super ba. 



The larvae in a sample of 243 individuals from St. 374 have been arranged in Table 

 XX in order of ascending size, and when of the same size roughly according to the degree 

 of development of various appendages. 



Length and telson. In Table XXI the larvae have been arranged according to their 

 length frequency. The succession of peaks presented is to some extent made intelligible 

 by distinguishing the larvae according to the number of spines on the telson. There is a 

 correspondence in position of the maxima in the length frequency of all the larvae with 

 those identified according to the telson spine number. Increase in size is accompanied 

 by reduction in the number of telson spines, but there is a great amount of overlapping 

 in the length range of any one telson spine group and the length ranges which succeed 

 and precede it. 



The reduction in the number of telson spines is brought about normally by the dis- 

 appearance of the outermost on either side so that the reduced numbers are 5, 3 and i. 

 This is not invariable, as the telson spine numbers 6, 4 and 2 indicate in Table XXI ; 

 but these forms are present in such small numbers in relation to those with 5, 3 and i 

 that they must be regarded as exceptional. Independent evidence in favour of such a 

 conclusion is provided by the frequency, as expressed by the number of stations at 

 which they were found, of larvae having the different forms of telson recognized. 



Thus: 



Larvae with 6 terminal spines occur at 5 stations. 



Several aberrant telson forms are referred to in the notes below the list on p. 53, 

 and some of these are figured (Fig. 12). In three of the figures of unusual telson form 

 the number of spines in the succeeding stage is shown — all three indicate that the 

 aberration of telson form persists when the larva moults. 



Telson spine numbers. In Table XXII are stated the length frequencies of larvae 

 arranged according to the number of telson spines in the succeeding stage. Here again, 

 in the seven-spined larvae as in earlier analyses, the smaller ones tend to moult again 

 into seven-spined forms and the larger into five-spined forms. In the five-spined larvae 

 similarly a few moult again into five-spined forms, and there is a surprisingly large 

 number with four spines, but the greater number moult directly into a three-spined 

 form. 



7-2 



