LARVAL DEVELOPMENT 257 



Those recognized by the number of terminal spines on the telson. In the five species, as 

 in E. stiperba, the path of development is usually one coincident with the reduction of 

 the number of terminal spines on the telson from seven to five, five to three and three 

 to one (Table I). Even numbers of terminal spines are abnormalities (Fraser, 1936, 

 p. 51), and individuals having them are not regarded as variants of the same value as 

 those of the earlier group with unusual numbers of pleopods. In E. triacantha only does 

 the first of these later stages have the original number of seven terminal spines ; in the 

 other four species it has been reduced to five.^ 



E. frigida \ 



E. vallentini \ I I I I I 1 -» I II II 1 -» OI 



E. triacantha 



^ ^ ^ ^ V V V V ^ vvvvv 



£. longirostris 1 , , , , , , _ | 1 1 | | | ^ | | | | | | -. | I I I I I 

 E.sptmfera \ \ \< < < \\\\< VVVV V 



Fig. 34. Diagram showing the paths of early Furcilia development in five species of Etiphausia. 



Explanation given in the text. 



The last of the Furcilia stages to be recognized by the number and character of the 

 pleopods have, in all except E. vallentini, seven terminal spines on the telson (except 

 for one E. frigida) ; in E. vallentini there are either seven or five or, exceptionally, six 

 spines. A number of this stage with seven spines and a number with five were examined 

 to see how many spines would be present in the succeeding stage. It could be seen in 

 very few of them. Of ten having seven terminal spines one was going to have six spines 

 after moulting, six five spines, one four spines, and two three spines;- of twenty with 

 five spines i appeared as though it were going to have five spines again after moulting, 

 17 were going to have three spines, and 2 two spines. It seems then that the majority of 

 those with seven terminal spines would have, after moulting, five spines, the majority of 

 those with five, three. It is, no doubt, for this reason that the number of individuals (20) 



1 In regarding the single Furcilia forms as stages I differ a little from Fraser. For example: 



His Furcilia I of E. superba is made up of forms with no pleopods, or with two, three, four or five pairs 

 of non-setose pleopods ; of these he saw in all the following numbers : 



With no pleopods ... ... ... ... ... ... 8 



With two pairs of non-setose pleopods ... ... ... 4 



With three pairs of non-setose pleopods ... ... ... 16 



With four pairs of non-setose pleopods .. ... ... no 



With five pairs of non-setose pleopods ... ... ... 942 



The sum of the three infrequently occurring forms (28) is 2-5 per cent of the total of all five forms (1080). 

 My Furcilia I of E. frigida, E. valtentini and E. triacantha is of individuals having four pairs of non-setose 

 pleopods. Of E. vallentini I saw sixty-two with four pairs of non-setose pleopods and none with any other 

 number. Of E. frigida there were 123 with four, one with three, and one with five pairs of non-setose 

 pleopods ; of E. triacantha 310 with four, five with five, pairs of non-setose pleopods. It seemed to me better 

 to record the infrequent forms as exceptions or variants, than to widen the definition of the stage so as to 

 include them. In both E. frigida and E. triacantha the percentage of the variants is i-6 per cent; it is less 

 than in E. superba, but in both based upon smaller numbers. In E. vallentini there were no variants. 



2 Lebour (1926c, p. 768) found in the "sixth furcilia" of Nematoscelis microps "specimens with seven 

 spines giving rise to three, which show under the skin ". 



D XIV 9 



