1911] Michael: Chaetognatha of the San Diego Begion. 147 



This table shows clearly that the species was practically never 

 obtained during daylight above 40 fathoms, while during the 

 night it occurred above this depth. While the difference between 

 day and night distribution is not so striking as in the case of 

 8. hipunctata, the data point in exactly the opposite direction to 

 those of Fowler (1905). In the Biscayan plankton he found S. 

 serratodentata more frequent on the surface during daylight. He 

 has, however, regarded the day as including twilight, while I have 

 regarded the night as including it. This, together with the fact 

 that in table 55 we find very little distinction between day and 

 night surface distribution, and that the number of specimens is 

 so small, may explain the difference noted. 



In connection with day and night distribution it is significant 

 to discover that, when data obtained with vertical closing nets 

 are segregated as in table 56, similar variation is found. 



