DEVELOPMENTAL PHASES 375 



Furcilia stages. Frost (1935) has already described one calyptopis, three furcilia and four cyrtopia 

 stages for this species. The calyptopis was a third calyptopis and she called the three furcilia the third, 

 eighth and penultimate. The cyrtopia were the first to the fourth inclusive. 



Gurney (1942) considers Frost's furcilia stages to be the first, second and third furcilia. Undoub- 

 tedly her ' third ' and ' eighth ' furcilia are in reality the first and second stages respectively, for no 

 preceding or intermediate forms have ever been found. In the present series, however, a form inter- 

 mediate between Frost's eighth and penultimate furcilia occurs. This form has five setose pleopods 

 and seven terminal spines on the telson. Only one specimen was found, but it is considered here as 

 the third furcilia stage. 



Frost's penultimate furcilia had the telson spines reduced to five. This now becomes the fourth 

 furcilia stage. Frost considered that this stage was not the immediate precursor of the first cyrtopia, 

 for in all other cases of euphausiid development there are two stages with only one terminal telson 

 spine ; in the first stage the long, outer laterals are present and in the second they are absent. She thought 

 it highly probable that one or more stages exist between her penultimate furcilia and first cyrtopia. In 

 this she was quite right, for one specimen was found in this series having one terminal telson spine 

 and still retaining the long, outer laterals. 



I have called this the sixth furcilia, however, rather than the fifth. If it were the fifth the number of 

 terminal spines would have to be reduced from five to one in one stage. This sequence has never been 

 reported in any other euphausiid life-history and it seems justifiable to suspect that there is at least 

 one stage with three terminal spines on the telson. The furcilia stages then are as follows: 



n. = non-setose, s. = setose ; stages 5 and 6 have the second antennal endopod segmented. 



The numbers of specimens in each stage in this series are as follows : stage 1 = 28, stage 2 = 48, 

 stage 3 = 1, stage 4 = 9, stage 5 = 0, stage 6=1. 



Frost's descriptions and illustrations are accurate and adequate and it is considered unnecessary to 

 elaborate on them. 



BIBLIOGRAPHY 



Boden, B. P., 1950a. Plankton organisms in the deep scattering layer. U.S. Navy Electronics Laboratory Rep., 186, pp. 1-29. 



19506. The post-naupliar larval stages of the crustacean Euphausia pacifica. Trans. Amer. micro. Soc, 69, pp. 373-86. 



195 1 . The egg and larval stages of Nyctiphanes simplex, a euphausiid crustacean from California. Proc. zool. Soc. London, 



121(3), PP- SiS-27- 



1954. The euphausiid crustaceans of southern African waters. Trans, royal Soc. S. Afr. 34 (1), pp. 181-243, 2 4 % s - 



Calman, W. T., 1896. On deep-sea Crustacea from the south-west of Ireland. Trans, royal Irish Acad. 31 (1), pp. 1-2 1, 2 pis. 



1905. Note on a genus of euphausiid crustacean. Sci. Invest. Fish. Ireland, 1902-3, 4 (ii), pp. 153-5, 1 pi. 



Chun, C, 1887. Die pelagische Thicrwelt in grosseren Meerestiefen und ihre Beziehungen zu der Oberfldchcnfauna. Biblio. Zool. 



1, pp. 1-66, 5 pis. 

 Colosi, G., 1917. Crostacei— Parte II. Eufausiacei. Racolte planktoniche fatte dalla R. Nave 'Ligura', 2 (7), pp. 165-205, 



3 P ls - 

 Currie, R., 1953. Upwelling in the Benguela Current. Nature, London, 171, pp. 497-9, 3 figs. 

 Dana, J. D., 1852. Conspectus of the Crustacea of the exploring expedition under Capt. Wilkes. Amer. ]. Sci. 13 (1), pp. 1-685. 



