240 DISCOVERY REPORTS 



All the specimens were fixed, and preserved in neutralized sea-water formalin, in most cases in the 

 whole plankton sample; this seems to give the best results. Chaetognaths removed from hauls before 

 fixation and preserved separately often fix in a bent or distorted position, and if placed upon formalin- 

 soaked blotting-paper to keep them straight, tend to get damaged. Specimens of S. gazellae preserved 

 in large plankton samples are usually in good condition, and samples consisting mainly of copepods 

 such as Rhincalanus gigas or Calanus propinquns nearly always contain perfect specimens of Sagitta 

 gazellae. The material from 70 cm. vertical nets is the most perfect, and the 70 cm. oblique nets yield 

 specimens in better condition than those from the 1 m. nets. Specimens from 2 m. and \\ m. nets 

 are often damaged, none being found with seminal vesicles intact, although the animals were of such 



Table 2. List of stations from which data were obtained during the present work 



Counts and measurements 



N70V Stations 2010, 2012, 2014, 2015, 2017, 2018, 2020, 2022, 2023, 2024, 2025, 2026, 



2027 



2311, 2313, 2316, 2318, 2320, 2322, 2355, 2356, 2357, 2358, 2359, 2361, 

 2385, 2386, 2387, 2389, 2391, 2393 



2424, 2425 



2492, 2494, 2495, 2496, 2498, 2501 



2530, 2531, 2532, 2533, 2535, 2538, 2541, 2543, 2545, 2547 



N100B Stations 414, 1774, 1775, 177° 



2312, 2313, 2316, 2318, 2320, 2322 

 2355, 2359, 2361, 2374 



2385, 2386, 2387, 2389, 2391, 2393 

 2424, 2425, 2426, 2428, 2430 

 2459, 2460, 2461, 2463, 2465 

 2492, 2495, 2496, 2498, 2500 



253 1 . 2 535. 2 53 8 > 254 1 . 2543. 2545. 2547 

 2606-2626 



2374-2379 (excluding 2376) 

 1 608-1 625 (excluding 1613, 1620, 1622) 

 1644-1664 (excluding 1649, 1650, 1656-1658, 1661) 

 1687-1699 (excluding 1691, 1692, 1698) 



TYF and N450 oblique Stations 391, 395, 401, 405, 413 



1298 



1702, 1707, 1715, 1718, 1719, 1723 



1871, 1876, 1917, 1919, 1944, I94 6 - J 966, 1970, 1972, 1974. !9 8 9. !99i> 

 1993, 1995, 2001, 2006, 2008, 2029, 2031, 2033, 2036, 2042 



TYF vertical Stations 661, 663, 666, 668, 669, 671, 673, 675, 677, 679, 681 



1154, 1156, 1158, 1160, 1165, 1167, 1173, 1175 



a size and stage of maturity that these structures should have been present. However, for the examina- 

 tion of hooks, teeth and ovaries, material from large towed nets is quite satisfactory. The ovaries are some- 

 times inadequately preserved, especially in the larger specimens, and cannot be accurately measured, but 

 this only occurs at the fourth stage of maturity (see p. 244) (when the ovaries are greatly swollen) ; the 

 thin rod-like ovaries of the earlier stages are always adequately preserved. Thus the stage of maturity 

 can always be determined, even if the degree of advancement of maturity within the stage cannot be. 



Considerable shrinkage takes place in formalin-preserved material (George, 1952) and as measure- 

 ments of freshly preserved material from the 1931-33 and 1935-37 commissions of 'Discovery II' 

 were available it has been possible to gain some idea of the extent. Unfortunately the degree of 

 shrinkage is not consistent, and it has not therefore been worth while making any corrections to 

 measurements to allow for it. Measurements of 100 specimens ranging from 20 to 105 mm. (freshly 

 preserved) show an average shrinkage of 7-25%. 



In 1 95 1 a few measurements were done on board ship to determine the extent of shrinkage during 



