OCTOBEE 1, 1920] 



SCIENCE 



309 



of a copepod on the same basis tliat one ex- 

 plains a similar habit in a chjetognath. 



2. There is something connected either with 

 the removal of specimens from the sea or their 

 retention in the laboratory, or with both, that 

 affects the responses in some cases. The rela- 

 tion between the behavior in the laboratory 

 and that in the sea is consequently obscured. 

 For example, the copepod, Calanus finmarclii- 

 cus, can be taken at twenty fathoms during 

 the day. When removed to the laboratory these 

 animals are positive to light for about an hour 

 on the average but become negative and re- 

 main so persistently. Is it not obvious that 

 such a reversal makes it difficult to know how 

 to apply experimental results toward explain- 

 ing the migration? This kind of thing did 

 not appear in all the species that I used, but 

 it oertaiuly should be looked for in all cases. 



3. Specimens of the same species, but ob- 

 tained from different locations or habitats, 

 show noteworthy differences in behavior. A 

 good example of this is found in the reactions 

 of a copepod, Acartia tonsa. If animals are 

 used that were obtained at the surface they 

 move toward the light, and they ascend in dif- 

 fuse light though they descend in darkness. 

 But if the specimens were obtained from deeper 

 water (60-100 feet) they move away from the 

 light and descend both in diffuse light and in 

 darkness. 



Suppose that one is attempting to explain 

 the diurnal migration of Acartia. The results 

 of experiments with surface animals would 

 lead one to expect to find the animals at the 

 surface during the day and at lower levels at 

 night. Wh-ile they may be found at the sur- 

 face by day at times, we have thousands of 

 collections which show that these copepods are 

 much more abundant at the surface at night. 

 It depends on the particular animals collected 

 whether it shall be said that Acariia tonsa as 

 a species is positive or negative to light. It 

 is worth noting in this connection that speci- 

 mens of A. tonsa from deep water, if left in 

 the laboratory for several hours, will react as 

 surface animals do. 

 ! 4. Need of experimental and field data to- 



gether. It does not seem possible that the 

 facts of nor the reasons for the diurnal mi- 

 gration (or any other natural habit) can be 

 obtained without both laboratory and field 

 studies. The results of work in the field will 

 show what the animals do in their natural sur- 

 roundings, while experimental work may show 

 why they act as they do. Experiments are in- 

 capable of revealing what occurs in a natural 

 habitat, unless it is possible to duplicate na- 

 ture in the laboratory and at the same time 

 secure experimental control. One can hardly 

 do better in this connection than to quote 

 what another has written: 



What right has one to assume that the reactions 

 of an animal taken rudely from its natural habitat 

 and as rudely imprisoned in some improvised oage- 

 are in any scientific sense an expression of its nor- 

 mal behavior either physical or psychical? Is it 

 within ifche range of the calculus of pr.obability that 

 conclusions drawn from observations made upon 

 an animal in the shallow confines of a fingerbowl, 

 but whose habitat has been the open sea, are trust- 

 worthy? . . . Laboratory appliances are indispen- 

 sable. But at the same time it must be recognized 

 that they are at best but artificial makeshifts 

 whose values, unless constantly checked by ap- 

 peals to nature, must be taken at something of a 

 dis'count.i 



Such statements as the foregoing ' can not 

 apply to experimental procedure that attempts 

 to ascertain what animals can do, for example, 

 or how sensitive they are to stimulation. 

 Strictly physiological studies are both neces- 

 sary and important and their brilliant results 

 more than justify them. But in such methods 

 of working the agent is emphasized rather 

 than the organism, and the aim is to " work 

 out the physics and chemistry of biological 

 phenomena."^ When, however, the organism 

 is the chief interest, the natural history of the 

 organism must be known if we are to study 

 nature instead of things in a laboratory. Lab- 

 oratory studies are of no more importance than 

 those made in the field if one's object is to get 



1 Charles W. Hargitt, Jour. An. Behav., 2, pp. 

 51-52, 1912. 



2 H. S. Jennings, Ainer. Jour. Psych., 21, p. 353, 

 1910. 



