288 University of California Puhlications in Zoology [Vol. 18 



E. SUMMARY AND CONCLUSIONS 



The facts revealed by this investigation may be summarized under 

 three heads as follows : 



I. Facts relating to seasonal distribution: 



1. The occurrence of Salpa democratica in the San Diego region 

 at all depths during 1908 and 1909 reached its maximum in the 

 summer, both generations being restricted almost exclusively to 

 the months of June and July. 



2. Both generations were more abundant on the surface during 

 June than during July. 



3. Aggregate forms were more abundant than solitary forms 

 during June, while solitary forms were the more abundant during 

 July. 



II. Facts relating to vertical distribution: 



1. Solitary forms are most abundant on the surface, decreasing 

 in abundance as the depth increases. 



2. Aggregate forms are most abundant in the neighborhood 

 of five fathoms, decreasing in abundance as the depth increases 

 below that level. 



3. Aggregate forms were, on the average, more abundant than 

 solitary forms at all levels. 



4. Individuals of neither generation have been captured below 

 seventy-five fathoms. 



III. Facts concerning surface distribution during June and July, 



1908 and 1909 relative to temperature of the water: 

 1. When the data are tabulated with respect to two tempera- 

 ture groups ranging in value from 15?9C to 18?3C and from 

 18?4C to 20?8C respectively, they show that: 



a. Solitary forms are most abundant but least frequent 

 in the warmer water. 



b. Aggregate forms are most abundant and most frequent 

 in the colder water. 



c. The frequency of solitary forms in both warm and cold 

 water is nearly identical with that of aggregate forms. 



d. These same relations hold when all the June and July 

 data are considered, when day hauls alone are considered, 

 when night hauls alone are considered, when only hauls made 



