242 



DISCOVERY REPORTS 



development of the gonads, and in dividing up the stages of S. gazellae I have adhered as nearly as 

 possible to the system proposed by Kramp (1939) for S. maxima, a closely related species. 



Specimens of S. gazellae at advanced stages of maturity are rarely taken, and there is no record of 

 any in the literature ; this rarity is due to the breeding migration to deep water (see p. 270). Even in the 

 extensive Discovery collections there are few perfect mature specimens, and although I have ex- 

 amined a large number of deep hauls in the collection I have only ninety specimens in the later stages 

 (III to V) of maturity. 



Previous records of S. gazellae have been only of comparatively immature animals from the upper 

 water layers, and the total absence of really mature stages led to the view that the most advanced 

 stages then found (stage II) were nearer full maturity than in fact they were. Ritter-Zahony (1909), 

 in the original description of the species, stated that the ovaries were knee-shaped and compressed, and 

 gave an impression of maturity despite their shortness; he also remarked that the seminal vesicles 



Table 4. Comparison of maturity stages for Sagitta maxima and S. gazellae 



were not observed, but evidently mature before the ovaries. In a later paper (191 1), in which he 

 redescribed the species, he said he had never observed a ripe specimen, and that the largest ovary (in 

 an individual 66 mm. long) did not reach the anterior fin. Jameson (1914), describing an individual 

 of 88 mm. in length from the ' Scotia ' collections, said ' the reproductive organs are prominent, but 

 they do not seem to be quite mature; the ovaries extend forward for a length of 16 mm.' Subsequent 

 work on the species has not included any reference to any stages of maturity, and it is evident that 

 only immature specimens have been taken. 



Kramp (1939) has tabulated the development of the gonads in S. maxima. Consequently in this 

 species the advanced stages are better known, and I have used Kramp's work as a basis for making 

 a similar table for S. gazellae. The two are given side by side in Table 4, and the similarities between 

 them are apparent. 



Stage I. This is inevitably a wide category, covering a range of development from the larvae to 

 those animals in which the ovary is quite recognizable and characteristically ' knee-shaped ', and the 

 testes quite large. 



