1923] Esterly: Marine Copepoda at La Jotta 419 



The opportunity for another possible fault in this series should be 

 recognized, namely, the method of collecting. The towing was done 

 by seven different men, some of whom took the night hauls while 

 others took the day hauls. Some worked on alternate weeks for a part 

 of the two years and others worked week after week consecutively. 

 It need hardly be said that changes in the personnel sometimes oc- 

 curred, so that new men had to work into the routine. There is no 

 doubt that it would have been better if the collecting could have been 

 done by the same two persons throughout the two years, but that 

 was impossible. Perhaps there really are variations in the size of the 

 catches, which are due to differences between the persons handling the 

 net ; but it seems very unlikely that in the long run such causes could 

 have had any appreciable effect upon the final results. If one were to 

 set about deliberately to obtain a larger or a smaller haul, practically 

 all he could do would be to tow the net for a longer or shorter distance, 

 or faster or slower. The understanding was that the net should be 

 pulled through the water only fast enough to keep the cone extended, 

 and no faster. This condition was easil.y complied with in the daytime, 

 but at night it was hard to tell whether the net was moving fast 

 enough. I know from experience that it would have been hard to 

 pull the net at the end of the pole much more rapidly than was 

 necessary to keep it extended. When we consider the large number 

 of hauls made and the length of time through which the series 

 extended, it is hard to see how personal differences could have affected 

 the general results. 



Night collecting was subject to a source of error that did not 

 affect the day towing. Sometimes in lowering the net into the water, 

 air would be caught in the peak so that the end holding the bottle 

 was out of water. This difficulty could be overcome in the daytime, 

 but it is hard to tell how often it happened without detection during 

 the night towing. It is certain, however, that we have hundreds of 

 night hauls that were taken with the net properly submerged. 



In connection with this work no account has been taken of possible 

 variations due to clogging of the nets. It is well known that new nets 

 catch more than old ones. Our nets were used as long as they were 

 not torn. If thought worth while, it might be possible to ascertain 

 whether there is any constant relation between size of catch and con- 

 dition of the nets, since the change from 'old' to 'new' is noted in the 

 log books. 



Such factors as depth of water due to tide, currents, wave action, 

 sand, wind velocity, and possibly other factors may have affected 



