THE REPRODUCTIVE SYSTEM OF E. SUPERBA 329 



male. The rostrum is bluntly pointed in the female and projects forwards to the 

 anterior margin of the eye, whereas in the male it is rounded and extends only over 

 two-thirds of the eye. 



The adult female has a pair of well-marked forwardly projecting lateral denticles 

 on the ventral margin of the carapace at the level of the second pair of thoracic legs. 

 There is only the slightest indication of such structures in the adult male, the denticles, 

 which are present in young specimens, diminishing with each successive moult. 



The epimera of the abdominal segments are large, flat and blade-like. In the female 

 they are produced posteriorly, in the male both posteriorly and anteriorly, except the 

 first pair which alone project posteriorly. The last pair are triangular in both sexes, and 

 are very large in the male. 



The eye-stalks are short and carry large well-developed eyes, which are slightly 

 larger in the male than in the female. 



The antennular peduncles are three-jointed and exhibit small sexual differences. These 

 have been described in detail by John (1936) in his paper on the genus Euphausia, so 

 that nothing further need be said here. 



The basal part of the antenna is divided rather indistinctly into two parts, the first 

 carrying the opening of the green gland and the second the antennal scale and flagellum. 

 In the female, the antennal scale is truncate, extending about one-third along the third 

 antennular joint. It carries a small sturdy denticle on its outer apex. In the male, the 

 scale is more rounded, extending to the end of the second antennular joint, with a 

 thinner, smaller denticle. 



The mouth-parts and thoracic legs are similar in both sexes, except the sixth pair of 

 thoracic legs in the female, the coxopodites of which are modified to form the thelycum. 

 This structure will be described in more detail later in the paper. The oviducts open 

 between the thelycum and the ventral surface of the sixth thoracic segment. In the 

 male the external genital pores are on the sternum of the eighth thoracic segment. 



The pleopods are all similar in the female, but in the male the first two pairs are 

 much modified to form copulatory organs, an account of the development and structure 

 of which will be given later. 



I do not propose to describe the external characters of E. siiperba in any more detail ; 

 they have been fully dealt with by Sars (1885) and subsequent workers. My object has 

 been to draw attention to the chief external differences between the adult males and 

 females. 



REPRODUCTIVE SYSTEM 



PREVIOUS WORK 



Until the publication of two important papers, one by Zimmer in 191 3 and the other 

 by Raab in 191 5, work on the reproductive system of the Euphausiacea was fragmentary. 



The first description of the system, though a short one, was given by Claus in 1868 

 of the genus Euphausia, together with a figure showing a spermatophore attached to the 

 ventral surface of the female "unter zwei vorstehenden Flatten". The work of Boas 



