114 University of CaliforHia Puhlicatious in Zoology. [Vol.8 



In this calculation it is assumed that both nets have the same 

 size of mesh, but this is not true. The mesh of the Kofoid net is 

 No. 000 and that of the Nansen net No. 1. Obviously, other 

 things being equal, more water will be filtered by the net having 

 the larger mesh, which means that W = less than w X 8. 

 However, owing to the fact that the nets are towed horizontally, 

 the exact effect of this difference in mesh on the amount of 

 water filtered cannot at present be calculated. The number of 

 specimens obtained from each depth by each net are, therefore, 

 uneorrelated and in the following discussion allowance must be 

 made for this fact. 



Finally, it is obvious that a surface net of 000 mesh with an 

 orifice of 97.5 cm. in diameter will filter more water than the 

 Kofoid net would if hauled in place of the former. Theoretic- 

 ally the amount of water filtered during a given surface haul 

 would be to that filtered by the Kofoid net as the s(iuare of the 

 radius of the former is to that of the latter. In other words, to 

 standardize the number of specimens obtained by the surface 

 net with that obtained by the Kofoid net the number ought to 



.... -, , (18.5)- = radius- of Kofoid net _-,., ., , . 



be multiplied by , .„ „^,., ^^ — t, — ^ ^ r While this 



(48.75)- = radius- ot surface net 



is theoretically required, the resulting fraction 1/7 is found 

 empirically to be far too large. Because this calculation is mis- 

 leading it seems best to allow for lack of correlation between 

 surface and closing net hauls and regard the average number of 

 specimens obtained per hour from the surface without attempting 

 correction. It will be found that the effects of varying environ- 

 mental conditions on the manner in which each species is distrib- 

 uted are apparent in spite of this lack of correction. 



Although ten species of Chaetognatha were taken from the 

 region of San Diego, lying between 32° 20' and 33° 30' N and 

 extending from the coast to 119° W, the region is characterized 

 by an enormous preponderance of one species. Including all 

 hauls from all depths the number of specimens of each species is 

 as follows: 



S. bipunctata 51,670 



S. enflata - 10,127 



S. serratodentata 6,575 



S. lyra 271 



S. neglecta 127 



