328 DISCOVERY REPORTS 



racters, if developed, were also noted. In all, 5564 specimens ranging from 16 to 64 mm. 

 were dissected, of which 2867 were males and 2697 females. 



Two series of sections, one longitudinal and the other transverse, were made of the 

 reproductive region of two adult females, each measuring 50 mm. and having spermato- 

 phores attached to the thelycum. The course of the oviducts was traced in these 

 sections, the more important of which were photographed microscopically (cf. Plates 

 II-V). 



Adult females were also used for a series of thick transverse hand-sections (about 

 I cm. thick) through the fifth, sixth and seventh thoracic segments, from which, after 

 further dissection, Fig. 23 was drawn. 



Finally, in order to determine the approximate number of eggs laid by one female, 

 the ovaries of two gravid females were removed from the body, and the eggs were 

 dissected out on to a large squared slide, separated from one another and counted. 



ACKNOWLEDGEMENTS 



I wish to acknowledge helpful criticism and advice from Dr Stanley Kemp, F.R.S. 

 and Dr W. T. Caiman, F.R.S., and to thank my former colleagues, F. C. Fraser and 



D. D. John, for their invaluable assistance and for permission to quote from their 

 papers and to reproduce certain diagrams. Dr N. A. Mackintosh has kindly allowed 

 me to make use of the colour notes in an original sketch by him of a living specimen of 



E. superba. I was thus able to make the coloured plate of a male and female specimen. 

 My colleague. Miss D. M. E.Wilson, has also helped me in very many ways, and I am 

 very greatly indebted to her practical interest throughout the work. 



EXTERNAL CHARACTERS 



Euphausia superba is shrimp-like in appearance, attaining when fully grown a length 

 of between 50 and 65 mm. The living specimens (PI. I) are remarkable for their 

 transparency and their bright coral-red pigmentation, which often makes the occurrence 

 of the large surface shoals of this animal very conspicuous. The body is covered with 

 a thin, chitinous exoskeleton, which, although much thickened after the final moult 

 before maturity, is always delicate enough to allow the internal organs and muscles 

 to be seen. The adult is thus not very heavily armoured, spines being present only on 

 the carapace and not on the abdomen, except for a well-marked pre-anal spine in both 

 males and females. 



The carapace is not very extensive in either sex, although the whole body of the adult 

 female is thicker, heavier and longer than that of the male. In a mature female 58 mm. 

 in length, the depth of the carapace measured 13-5 mm. and the width 6-5 mm., whereas 

 in a male 56 mm. long, the depth of the carapace was only 9 mm. and the width 4-5 mm. 

 The ventral margin of the carapace does not overhang the bases of the legs, and the 

 gills which project freely into the water are more exposed in the male than in the female. 



In the adults of both sexes there is a spine on each anterior, lateral corner of the 

 carapace, this spine being sharp and long in the female, and blunt and short in the 



