THE OSTEACODA. 305 



Simultaneous and consecutive Hauls. --f-.^ 



It was not realised when the Biscayan cruise was planned how complicated are the K^ 



movements of the epiplankton. My aim was, to get at least one haul at every hour of /> jjP 



the twenty-four at every depth (0, 25, 50, 75, 100 fm.), and more than one at the depths i^i L I B R A 



'"*- ■^k-.-e-ta, 



and hours which were helieved to be " critical " : this plan was almost completely carried 

 out; and in a case where mesoplankton hauls have also to be attended to, where time is ^^ *tao^''- . 



limited and workers are few, it is about as much as can be done to fit the epiplankton >^i__J^ji 



hauls into the intervals of the mesoplankton work *. But it has become apparent in the 

 course of these investigations that simultaneous hauls at the different horizons would 

 probably in many cases have been more insti'uctive. Of these there were taken com- 

 paratively few, but they are significant as showing the " stratification " of species at 

 difi'erent depths and hours. A few examples of such hauls are given in the table 

 (p. 306), which illustrate various points. 



In the hauls, 30 m, 30 /, 31 a, 31 b are examples of simultaneous hauls at 25 and 50 

 fathoms, taken in two consecutive hours. Both hauls at 50 fm. show nearly the same 

 species, the hauls at 25 fm. show little or nothing else than curta. This is a good 

 example of that stratification which ought to be (but is not) universally recognised 

 as a natural corollary of the admitted stratification of physical conditions. What- 

 ever may have been the decisive conditions at 25 fm., it is quite obvious that 

 curta liked them and that other species did not. 



In the next series, 32 m, n, o,p, taken at a time of night and at the horizons where 

 the fauna is thickest, a similar stratification is shown, not in the species, but in the 

 number of specimens of those sjoecies at the two levels. 



In the third case, 35 y, 35 x, 3G a, 36 b, the paired hauls were in the same night, but 

 not in consecutive hours : the interest of these lies in the fact that the first pair were 

 taken between 7.0 and 8.0 p.m. at the beginning of the dark hours and show few or 

 no specimens of those species for Avhich on other grounds a nocturnal rise into the 

 epiplankton has been inferred {daphnoides, elegans, Jnjaloplitjlluiu, imbricata, spinifera) ; 

 the second pair, on the other hand, were taken in full niglit (11.30 p.m. to 12.30 a.m.) 

 and include all these species. 



The fourth example, 25 e, g, shows the difference between two hauls at the same depth 

 at an interval of 2^ hours ; the later haul apparently struck a " swarm " of magna and 

 A larvee, which had vanished again from that horizon before 2.0-3.0 a.m. of the same 

 night (25 k). 



Saul 27 a and Open Vertical Nets. 



This non-comparable haul from 1250-0 fathoms (a length due to the mesoplankton net 

 having opened but not closed) has been worked out in detail, and illustrates the 

 impossibility of learning anything of the real distribution of plankton by means of 



* In a swell, the manoeuvring of the ship, in order to keep the wire rope of the mesoplankton net vertical, often 

 made it impracticable to work epiplankton nets simultaneously. 



