xvi University of California Publications in Zoology [Vol. 15 



Together tliey are omnipotent; disjointed, they become impotent 

 fetishes. The biology of today . . . has not too mueh laboratory, but 

 too little of living nature." 



4. Complexity op Hydrobiological Rel.\tions 



On June 17, 1909, four surface hauls (p. 160, hauls 1659-1662) 

 were made off La Jolla with the same net wliile the "Agassiz" was 

 tied to its mooring. The temperature of the water was 18?4 C during 

 all four hauls. Yet, the first haul (5:00 to 6:00 p.m.) caught thirteen 

 specimens of Sagitta bipunctata, the second (6 :00 to 6 :45 p.m.) caught 

 none, the third (6:45 to 7:30 p.m.) caught 550, and the fourth 

 (7:30 to 8:00 P.M.) caught none. Thus, the number of specimens 

 varied erratically from none to 550, and the third haul caught about 

 fifty-six times more per hour than the first, an increase of fifty-six 

 hundred per cent in one hour and a half. It is evident, from the 

 constancy in temperature, that the current, and hence the volume of 

 water filtered, could not have varied to an extent corresponding, even 

 roughly, to the difference in number of specimens obtained. ]\Iore- 

 over, it is iinlikely that any progressive hydrographic change asso- 

 ciated with such a brief time interval could have cau.sed first a decrease, 

 then an increase, and finally another decrease in number of specimens 

 obtained. 



Someone may see in this example a demonstration that hydro- 

 graphic investigations can jdeld little definite information concerning 

 the relation of this species to the conditions of its environment. Does 

 not the instance prove this species to be erratically distributed with 

 respect to temperature and other hydrographic conditions; that the 

 condition of the environment had nothing to do with the variability 

 noted? On the face of the matter it seems so. Yet it is fairly well 

 established that Sagitta bipunctata is definitely affected by fluctuations 

 in the temperature of the water. On the surface it decreases in abun- 

 dance, on the average, as the temperature increases above 16° C. 

 Furthermore, every depth thus far investigated (5, 10, 15, 30, 40 and 

 50 fathoms) shows that the species increases in abundance as the 

 temperature increases from 9° C to 14° C, and decreases as the tem- 

 perature increases from 16° C to 21° C. In other words, the species 

 maintains a maximum abundance when the temperature lies some- 

 where between 14° C and 16° C. in spite of the fact that the above 

 instance gives no indication of it. The fact that one case apparently 



