54 University of California Publications in Zoology [Vol. 19 



ing the day at about 270 meters (Esterly, 1912, pp. 304-305), and 

 according to McEwen (1916, pi. 34) the mean annual temperature at 

 that depth is between 8° C and 9° C ; at such temperatures in the 

 laboratory the phototropism changes from negative to positive and 

 the geotropism from positive to negative. If it is assumed that when 

 the animals in the ocean reach water of 10° C they begin to ascend, 

 the ascent into warmer water remains to be accounted for ; this point 

 is not covered by the experiments. We know, however, from the field 

 records that Metridia is found in great numbers at the surface when 

 the temperature is 19° C (Esterly, 1912, p. 306). If the ascent begins 

 in a region of lower temperature, why does it continue into water of 

 temperatures in which experimental animals are positively geotropic? 

 It is possible that the answer to this question will be found in the 

 occurrence of a physiological rhythm, but I have no evidence that the 

 rhythm is present in Metridia. 



Reactions of the chaetognath Sagitta bipunctata 



A study of the reactions of this animal seemed especially desirable 

 because of the striking results obtained from the field data, as shown 

 by the study made by Michael (1911). He has shown that there is 

 marked correlation between occurrence of this species and variations 

 in certain external conditions, and the question at once arose whether 

 similar behavior would be shown in the laboratory. 



So far as I am aware, a chaetognath has never before been used in 

 experiments on behavior. Sagitta is usually to be obtained at La Jolla 

 in sufficient abundance if the collecting is done at depths of 75-100 

 meters. The animals come far enough toward shore to be taken from 

 the pier, but occurrence there is exceptional. 



A great deal of difficulty was experienced in obtaining specimens 

 in the proper condition for experiment. On many occasions they 

 show signs of morbidity even before they reach the laboratory. The 

 body becomes slightly opaque or milky and bits of sand and debris 

 adhere to the exterior. Moreover, the animals rest quietly on the 

 bottom of the dish if they are in bad condition, instead of swimming 

 around constantly. I soon learned that an animal that has sunk to the 

 bottom will not react. 



The reasons for the appearance of such unfavorable states are not 

 clear. Our success was much better if a two-quart jar was tied into 



