80 



DE. G. H. FOWLEE— BISCAYAN PLANKTON : 



From this table it may be inferred that Chsetognaths were less plentiful (or more 

 migratory) between and 50 fathoms : that the population increased down to 100 fathoms 

 at least. Below tliat level the hauls were scanty and the figures therefore are much less 

 reliable: not only so, but it must be remembered constantly that these open nets, 

 and especially the deeper hauls, pick up a large quantity of specimens on their upward 

 journey which belong to shallower horizons *. The 250-fathom hauls, for example, 

 represent not only the captures in an hour's slow horizontal towing (say a mile and half), 

 but also those of 250 fathoms vertical towing at a greater pace — a very considerable 

 addition. Now it is a fair inference from the above, that if the population below 

 100 fathoms were as large or larger than at that horizon, the average captures should 

 number considerably more, whereas, except in one instance f, they are less than at 

 100 fathoms. Hence we may conclude that the' population diminishes below 100 fathoms 

 or thereabouts. This conclusion is confirmed by the more accurate method of the 

 closing-net. 



ii. Hauls with the closing-net. 



Between 



150-50 



200-100 



250-150 



300-200 



400-300 



500-400 



750-500 

 1000-750 

 1250-1000 

 1500-1250 

 2000-1500 ) 



5 





16 

 42 



5 



6 



9 

 10 



16-4' 

 11-2' 



1-2' 







1-2 = 



B 



CO 



3 



1 



6 

 2 

 3 

 3 

 3 

 4 

 3 

 3 

 

 1 



►tJ 





1 



7 

 3 

 3 

 3 

 3 

 4 

 5 

 3 

 2 

 2 



^ i- 



CO 3 



!=; ^ 



o ^ 



Op 

 -tj <! 

 P fD 



V P 

 o a^ 



5 ™ 



Ui 00 

 CO 



B 



CO 



s 



/ 



16-0 

 60 

 1-6 

 2-0 

 3-0 

 3-3 

 41 

 2-2 

 0-4 

 00 

 0-6 



' Number captured divided by 2-5. 



Number captured divided by 5-0. 



The sudden drop in the last column after 200 fathoms is most instructive : from 200- 

 1000 fathoms the figures are small, but as steady as could be expected from the com- 

 paratively small number of hauls. Below 1000 fathoms is apjmrently another drop ; 

 but even at this deepest stratum there can be no question of the j)resence of quite large 

 numbers of Chaetognaths even at the lowest depth investigated ; for example, the three 

 hauls 1250 to 1000 fathoms filtered only a cube of about 16 feet each, but produced 

 one specimen each. Haul 26 b (2000-1500 fathoms) was towed at about 1900 fathoms 



* Of course exactly the same criticism applies to my hauls with open nets at 25, 50, 75, and 100 fathoms ; but 

 with much less force, for these hauls were only towed upwards through a small fraction of their horizontal tow 

 (instead of a largo one), and were made in such numbers as practically to eliminate error by comparison. Below 

 100 fathoms the ratio of vertical to horizontal tow becomes serious, unless very prolonged horizontal hauls be taken, 

 which is bad for the material captured. 



t Namely 250 fathoms. Of the two hauls concerned, the one contained considerably more (72), the other 

 considerably less (29), than the average for 100 fathoms. 



