1914J Esterly: CtenopJiora of the San Diego Region 25 



The distribution of surface hauls by months is shown in table 3, 

 together with the numbers of hauls that contained Pleiirohrachia and 

 the number of animals in each month. 



TABLE 3 



Distribution of Surface Hauls by Months, Number of Hauls Containing 

 Pleurobrachia, Total Number of Animals Obtained 



Month 

 February 

 March 



Total 

 Hauls 



16 



30 



Successful 

 Hauls 



5 

 4 



Number of 

 Pleurobrachla 



143 

 23 



Agril 

 June 



13 



83 



6 

 13 



360 

 813 



July 

 August 



40 

 43 



5 

 25 



' 30 

 6500 



September 

 October 



6 



20 



2 

 



251 

 



November 



6 



4 



81 



December 



17 



8 



139 



Table 3 shows that there is a marked seasonal variation in abund- 

 ance, many more animals being obtained in August than in any other 

 month. The question at once arises : What makes August the most 

 favorable season of the year? The hydrographic conditions, such as 

 temperature or salinity, may be at the optimum then ; if so, that fact 

 should appear in the data on record. On the other hand, the time 

 when the organisms appear in greater numbers is undoubtedly re- 

 lated to the time of reproduction and to the growth periods, so that, 

 generally speaking, the animals will, under most circumstances, appear 

 in maximum numbers at a given time after the production of eggs. 

 It is, however, not unreasonable to assume that certain environmental 

 conditions are more favorable from the very fact that the organisms 

 are found in overwhelmingly greater numbers at a certain time of 

 the year. 



So far as I have been able to discover, there is nothing in the 

 literature that deals with periods of reproduction and growth in 

 any of the Ctenophora. And up to the present I have failed to find 

 anything in our collections or field data that will show when eggs are 

 produced or how long it is until the animals reach the adult stage. 

 It seems necessary, then, on account of lack of knowledge with regard 

 to breeding habits, to consider the relation between abundance and 

 conditions that are taken account of in our present methods of in- 

 vestigation. 



