2 S4 DISCOVERY REPORTS 



antarctic waters in profusion, then it might be expected that a similar colonization would have taken 

 place in the Arctic, as there is ample opportunity for specimens to be carried north by the North 

 Atlantic drift especially since the so-called 'intermediate' S. lyra "gazellae" -type has been reported 

 from various parts of the northern hemisphere. 



From the various points discussed above it may be concluded that S. gazellae Ritter-Zahony is a 

 species in its own right, which can be distinguished from all the varieties of S. lyra Krohn. 



RACIAL CHARACTERISTICS 



The surface layers of the Southern Ocean are divided into two main areas, the Antarctic zone, and the 

 Subantarctic zone. The line which divides these areas is the Antarctic Convergence, which is the point 

 where the Antarctic surface water sinks beneath the Subantarctic surface water. The division is, in 

 most areas, sharp and distinct, and is to some extent a faunistic boundary (Hart, 1934; John, 1936). 



Examination of a series of hauls made from the Subantarctic across the Convergence and into the 

 Antarctic zone, reveals striking differences in the appearance of S. gazellae on each side of the Con- 

 vergence. In the Subantarctic, specimens are found at advanced stages of maturity when 60 mm. in 

 length, whereas specimens of the same length in the Antarctic are found to be immature; in the 

 Subantarctic surface waters no specimens are found at a length greater than 68 mm., yet in the 

 Antarctic surface waters specimens of more than 90 mm. are quite common. 



In an unpublished progress report written on board R.R.S. 'Discovery II', in 1932, Mr Marr 

 suggested that the Antarctic and Subantarctic populations of S. gazellae are two separate races ; and 

 by a thorough study of the state of maturity of the various size groups was able to differentiate the two 

 races in areas where they mixed, notably in the Scotia Sea (especially south-east of the Falkland Islands) . 



The stages of maturity which he used prove to be subdivisions of the stages which I have called 

 I and II (pp. 242-3). Marr's stages are distinguished from mine by the use of arabic numerals 1 and 2, 

 and letter X, whereas I have used roman numerals 1 , 1 1 , etc. Fig. 1 4 shows these stages diagrammatically . 



There are three stages of maturity of the tail segment. Stage 1 includes specimens with small visible 

 rudiments of the testes up to specimens in which these rudiments extend to the transverse septum. 

 Stage 2 is usually characterized by the curl of the testes across the anterior end of the tail segment. 

 Stage X is equivalent to my stage II (p. 243). The tail segment is full of sperm and is opaque. No 

 further stage was found as no further development takes place in the surface layers (the deep-breeding 

 habits of S. gazellae were not known at the time when this system was devised) though the presence 

 of rudimentary seminal vesicles was noted in the most advanced specimens. Marr also noted the state 

 of maturity of the ovaries. These stages depend on the relative sizes of the transverse to the longi- 

 tudinal portions of the ovary. In S. gazellae the ovary opens on the dorsal surface, and its posterior 

 part extends towards the ventral surface at right angles to the long axis of the animal before con- 

 tinuing ventrolaterally along towards the head of the animal. This is the characteristic 'knee-shape' 

 described by Ritter-Zahony (1909, 191 1). 



Marr's stage 1 included animals which had visible rudiments of ovaries, and all intermediate stages 

 up to the stage where the longitudinal part of the ovary equalled the transverse part in length. The 

 upper limit of his stage 2 was reached when the longitudinal part was double the length of the trans- 

 verse part, and so on up to stage 4. In the surface waters animals were seldom found with ovaries 

 more mature than stage 4. 



Marr often recorded these stages as ' weak ' or ' strong ', according to their degree of maturity within 

 the stage. Animals in which no rudiments of the gonads were visible were recorded as immature, and 

 given no stage number. 



