ii6 DISCOVERY REPORTS 



tween 1-34 and 2-01° C, at St. WS 197 it is 1-33-1 -27° C, and with like positive tem- 

 peratures for Sts. 618, 620, 636, 637 and 648. With regard to the last station, at which the 

 larvae were found in each of the four nets from surface down to 500 m., it may be that 

 the warm surface temperature, due to the proximity of the station to the convergence, 

 produced the same favourable conditions for spawning and subsequent development as 

 are more generally to be sought for in the warm deep layer below 250 m. 



The significance of the vertical distribution of the Metanauplii is considered in con- 

 junction with that of later larval forms on p. 163. 



Later stages of development were present at all the stations where Metanauplii 

 occurred, and it is interesting to compare their vertical distribution with that of the 

 Metanauplii. In this comparison Sts. 639 and 648 have been regarded as exceptional 

 and the distribution of the larvae taken there is not represented in Fig. 33. At the former 

 station two Metanauplii were found, both in the surface net, and at the latter this stage 

 was present from the surface down to 500 m., with greatest concentration between 100- 





Fig. 33. Diagram showing the vertical distribution of the Metanauplius and later stages of development at 

 the stations indicated. Areas shown in outline represent the Metanauplius, areas in black represent later 

 stages. 



50 m. In the remaining seven stations, as shown in Fig. 33, the Metanauplii are con- 

 centrated in the lowest nets fished. With the exception of two individuals all are in the 

 750-500 m. and 1000-750 m. nets. It will be seen that there is considerable variation 

 in the vertical distribution of the older larvae and that this can be connected with the 

 time of day at which the net hauls were made. The stations have been arranged in a 

 sequence from midday to midday, the first starting at 1907 and the last finishing just 

 after midday. The figure shows that in the larvae of E. siiperba subsequent to the Meta- 

 nauplius stage there is a definite diurnal migration, so that during the hours of darkness 

 they are concentrated between the surface and 100 m., whereas at other times they are 

 massed at 500-250 m. The vertical migration of larvae will be referred to more fully 

 later ; it is sufficient here to mark the contrast between the behaviour of the Metanauplius 

 and subsequent larval stages. 



