4 University of California Publications in Zoology [Vol.19 



tion. Such work has shown, we believe, that the vertical movement is 

 wide spread among plankton organisms found in the San Diego region, 

 and that the conditions and factors involved make a problem of great 

 complexity. Studies of the field records indicate that it is possible to 

 ascertain without recourse to experiment some of the relations exist- 

 ing between external conditions and the movements of the animals. 

 Such studies, as carried on at the Institution, involve a large amount 

 of statistical and mathematical work (Michael, 1916, p. xix). It is 

 difficult to carry on the field and experimental work at the same rate, 

 so that experimental results will be considered for the most part at 

 this time. Some papers have already appeared dealing with the field 

 results (Michael, 1911, 1913, Esterly, 1911, 1912) and others are in 

 course of preparation. The published papers are based on statistical 

 methods that as a rule give trustworthy and significant results. In 

 some cases, however, the field data are inconclusive, and the experi- 

 ments were not completed on some of the forms. It has seemed desir- 

 able, nevertheless, to point out in this paper the possible relation 

 between the experimental results and the behavior in the sea as we 

 understand it from our field data. Statements about this relation are 

 more or less speculative, however, since both the field and experimental 

 data are lacking in certain respects. 



METHODS AND MATERIAL 



The laboratory procedure and apparatus were purposely as simple 

 as possible. Most of the work was done in a room with black walls. 

 Daylight entered the room through a north window 50 by 40 cm., and 

 this area could be reduced by means of a curtain and shutters of 

 different sizes. Artificial light was obtained from Mazda lamps. The 

 lamp in use was enclosed in a housing of black sheet iron. The rays 

 from the bulb passed out through a filter of Corning "Daylite" glass, 

 which according to Gage (1915) gives the electric light a quality 

 closely approaching that of daylight. The lamps were 15-watt and 

 100-watt, the latter gas-filled and with a concentrated C-shaped fila- 

 ment ; the opening in the housing of the former was 38 mm., in diam- 

 eter, of the latter 46 mm. The relative intensities of the different light 

 were determined roughly by means of a method suggested by Dr. G. P. 

 McEwen. Two blocks of paraffine of the same thickness were clamped 

 together with opaque cardboard between. The blocks were placed 

 between the lights to be compared and by suitably varying the distance 

 of the light from the paraffine it was possible to obtain approximately 



