1911] Michael: Chaetognatha of the San Diego Region. 1-15 



7. All individuals do not react toward light, temperature, and 

 salinity in the same way. While the majority migrate toward 

 the surface during twilight hours, and toward deeper water dur- 

 ing intense light and darkness, a few almost always remain in 

 deeper ivater during twilight, and on the surface during intense 

 light and darkness. Similar individual differences occur with 

 respect to temperature and salinity. This means that those 

 optimum conditions favorable to the species as a whole are not 

 favorable to each individual or, in other words, the characteristic 

 organization, constitution, or physiological state of each indi- 

 vidual modifies the effect of light, temperature, and salinity on 

 its behavior. 



DISTRIBUTION OF S. SEEBATODENTATA. 

 Of the 6,499 specimens of this species obtained, 76 were taken 

 from the surface, 676 in open vertical nets from depths varying 

 from 500 to 25 fathoms, 5,299 in vertical closing nets from 

 between 300 and 10 fathoms, and 448 in horizontal closing nets. 

 The 76 obtained from the surface were distributed in 14 or 9.5 

 per cent of the 148 hauls made. Of 68 vertical closing net havils 

 46 or 68 per cent obtained some specimens, while of the 118 hori- 

 zontal closing net hauls 33 or 18 per cent were successful, and of 

 41 open vertical net hauls 14 or 34 per cent obtained the species. 

 ]More complete data concerning the surface and closing net hauls 

 are given in the following tables. 



TABLE 53 



Vertical Distribution of S. serratodentata based on Surface and Horizontal 



Closing Net Hauls. 



