70 University of California Publications in Zoology [Vol. 19 



creased; there is some reversal in cold water (10° C), especially when 

 the light is above ; there is some evidence of a rhythm in the reactions 

 of specimens kept in very dim light, but only in ease the bottom water, 

 at least, is chilled. Eucalanus: strongly positive at ordinary tempera- 

 tures except when lighted from below, then strongly negative ; behavior 

 at low temperature not known ; possibility of rhythm not investigated. 

 Labidocera: it is safe to say that there is a tendency to negative form 

 of response in darkness and to positive in diffuse light ; strongly nega- 

 tive in light from below, strongly positive in light from above ; behavior 

 at low temperatures unknown, and existence of rhythm not investi- 

 gated. Metridia: at ordinary temperatures it is strongly positive in 

 darkness and in all conditions of lighting except from below, then 

 strongly negative; the behavior shows reversal at low temperatures; 

 existence of rhythm not investigated. Sagitta: if light is not too 

 bright there is marked negative geotropism under all conditions and 

 in darkness; in bright diffuse daylight the response is markedly posi- 

 tive; the animals do not descend in cold water, but the ascent occurs 

 in darkness out of cold water as well as out of warmer. 



There are of course similarities in the behavior of different forms, 

 and this is to be expected. For instance, Calanus, Eucalanus, Labi- 

 docera and Metridia are negative to light at room temperatures; 

 Acartia and Sagitta are positive ; Calanus and Metridia become positive 

 on cooling, Acartia becomes negative. It is recognized that the experi- 

 mental work is incomplete, particularly in that the behavior of Euca- 

 lanus and Labidocera in cold water is not known. But even so, if the 

 behavior as a whole, or the sum of the responses, is considered in the 

 cases of Acartia, Calanus, Metridia, and Sagitta it is very clear that 

 each species has its own mode of action. It is possible, of course, that 

 as more is known about the responses of the different forms the differ- 

 ences will tend to disappear ; and it is likewise possible that when more 

 is known still other differences will appear. But as the results stand 

 it is plain that a general explanation based on laboratory responses 

 can not be given that will cover the diurnal migration for the different 

 species. Such an explanation is desirable, but it is necessary to recog- 

 nize that when many different kinds of organisms perform depth migra- 

 tions, it is likely that the end results are due to quite different causes. 



The matter of specificity in behavior has been referred to in publi- 

 cations from the Scripps Institution that deal with the result of field 

 investigations. Michael (1913, pp. 32, 36) has shown that manner of 

 distribution is as much a specific character as structure ; and he refers 



