62 DISCOVERY REPORTS 



proceeds, whereas in E. frigida division of the peduncle coincides with an increase in 

 the number of flagellar segments. 



Fig. 13. Development of the antenna (x 46). 



a, larva with 5 telson spines; c, larva 9-71 mm. long with 3 telson spines; 



b, larva 9-16 mm. long with 3 telson spines; d, larva 11-30 mm. long with 3 telson spines. 



In the statement of the number of segments in the inner ramus of the antenna of the 

 larvae from St. 374 (Table XX) the number has 

 been expressed as the sum of two, of which the 

 first indicates peduncular and the second flagel- 

 lar segments. 



In Table XXIII the length frequency of the 

 larvae according to the number of terminal 

 spines in the telson and the state of the inner 

 ramus of the antenna are given. None of the 

 seven- or six-spined larvae possess segmented 

 antennal inner rami. Among five-spined larvae 

 89-7 per cent have unsegmented and 10-3 per 

 cent have segmented antennal inner rami. 



The number of four-spined larvae is incon- 

 siderable but all have segmented inner rami. By 

 the time the larvae are three-spined, only a very 

 small minority are unsegmented, and in the two- 

 and one-spined larvae no unsegmented antennae 

 occur. The analysis shows therefore that the 

 change in the form of antenna is not restricted 

 to one stage but may take place in five-spined or Fig. 14. Segmentation of antennal inner ramus. 

 three-spined larvae. It also shows that, within a,Thysanoessa maoura; b,Eiiphausiafrigida; c, 



E. siiperba. Diagrammatic, a and b after Rustad. 



