DISTRIBUTION OF ANTARCTIC MACROPLANKTON 91 



throughout the day, and it is very improbable that there is any real variation. The dis- 

 tribution of this species at St. 461 strongly suggests that there is no variation. 



Pyrostephos vanhqffeni (Fig. 20). The curve is actually made out for the numbers of 

 nectophores, and not the individual colonies. It is a patchy species and the peak at 

 midday is due to only one station, at which an abnormal number occurred. The actual 

 occurrences are equally distributed through the 24 hours, and the species can be regarded 

 as having no significant diurnal variation. 



Sibogita borchgrevinki (Fig. 20). Only fifteen specimens were taken north of 6o° S, so 

 that a reliable curve cannot be drawn. The fifteen were spread equally through the day 

 and night, but the stations at which it was counted as absent were mostly day stations. 

 Several specimens occur at St. 461, but there is no sign of any vertical migration. 



Solmundella sp. (Fig. 18). This is not a very common form, but in contrast to the four 

 preceding species, it has a very clear diurnal variation, no specimens having been taken 

 in the daytime between 0500 and 1859, except in high latitudes. It is not represented 

 at St. 461. 



Tomopteris sp. (large) (Fig. 19). There is a slight suggestion of variation, about 

 equivalent to that of Calanus aattus, but it is not of much significance. No conclusive 

 results are to be found in St. 461 or in Sts. 618-25. 



Tomopteris sp. (small) (Fig. 19). Similar to the large Tomopteris. All these curves 

 which show a slight variation have peaks which might be regarded as accidental, were 

 they not all at or near midnight. 



Vanadis antarctica (Fig. 20). As in the case of Sibogita we have insufficient material 

 for a trustworthy curve. The genus is recorded at only thirteen stations north of 6o° S. 

 They are spread throughout the day, so that there is not likely to be any very significant 

 variation. On the whole slightly more specimens were taken at night. 



Auricidaria antarctica (Fig. 20). Again there are very few specimens north of 6o° S, but 

 these show no sign of any variation ; nor do those from farther south. It must perhaps still 

 be regarded as a doubtful species, but any important diurnal variation is very unlikely. 



Calanus acutus (Fig. 19). The averages of a large number of hauls and vast numbers of 

 specimens show a slight diurnal variation. The species, however, is taken at all hours, and 

 some of the biggest catches have been in the daytime. There is perhaps a faint suggestion 

 of a tendency towards vertical migration at St. 461, but there is no sign of any variation 

 at Sts. 168-25, and it: ma Y for the P resent be regarded as a species without significant 

 diurnal variation. 



Calanus propinquus (Fig. 19). The exact amount of diurnal variation cannot properly 

 be estimated without a very large body of data. There is evidently rather more than in 

 C. acutus, but the largest hauls of this species also can be taken in daytime as well as at 

 night. St. 461 gives no definite indication, but Sts. 618-25 confirm the existence of 



some variation. 



Calanus simillimus (Fig. 18). The curve shows a clear variation. The species has been 

 caught at nearly as many day stations as night stations, but the night catches are larger. 



It is not represented at St. 461. 



4-2 



