NORTH ATLANTIC PLANKTON. 



37 



jfl«*H*? 



1** 



ft= 



•a *«t insuU 

 !. net o<»tsi^«. 



charge becomes somewhat intermittent — sudden rushes 

 caused by the surging of the water in 

 the tank alternating with a more 

 steady flow. These great rushes of 

 water led to the damage of some of 

 the specimens collected in the coarser 

 ^V fifi Cw « ,.* ~.uu net on the overflow pipe — this was 



Xj m F,u«t.^, especially the case with the Amphi- 



poda, Schizopoda, and larger Cope- 

 poda. As similar specimens were 

 not so much damaged in the nets 

 at the tap on the port side, we 

 may conclude that little or no dam- 

 age is received in passing through 

 the pump. 



With the help of the carpenter I 

 made an estimate of the amount of 

 water passing through each of my 

 nets during the period of time for which they were set. At 

 the tap, when turned on to the extent which I found 

 could just enable the water to get away through the nets, 

 four gallons passed out in 45 seconds, which is about 

 3,600 gallons in the 12 hours. At the overflow pipe I 

 found that, on the average, about 21,600 gallons passed 

 in the 12 hours, so these overflow nets strained six times 

 as much water as did those on the tap. This, of course, 

 accounts for the much larger quantity of material usually 

 caught by the starboard nets. The difference in size of 

 mesh between the two sets of nets also, no doubt, caused 

 some difference in the results. A further cause of differ- 

 ence was this : — the tap was supplied by a pipe coming 

 from a rose inserted near the bottom of the tank, while 

 the overflow pipe left the very top of the tank, and so 

 carried off the surface water. I noticed frequently that 





Fig. 4. 



