110 University of California PuhUcations in Zoology. [Vol.8 



3. To accomplish this, hauls at all depths should be repeated 

 as often, and under as great a variety of conditions as possible. 



4. It is advisable, if not necessary, to plan all collecting with 

 respect to one problem at a time; otherwise the data will be too 

 indefinite to permit accurate conclusions. 



5. Emphasis should be laid upon method of collecting rather 

 than on quantity of plankton obtained, for an ounce of plankton 

 collected systematically under known conditions, and with 

 respect to definite problems means more than a ton otherwise 

 obtained. 



In conclusion, all the significant data concerning the distri- 

 bution of the Chaetognatha so far obtained is condensed into the 

 accompanying table, from which we may provisionally split the 

 order into four groups according to temperature relations. 

 These groups are as follows : 



1. Eurythermal species, distributed irrespective of tempera- 

 ture. This group includes *S'. hipunctata, 8. liexaptera, S. plank- 

 tonis, S. serratodentata, and E. suhtilis. 



2. Cold water species^ temperature 16 ?0 to 0!0 or less. This 

 group includes S. sihogae, S. macrocephala, S. elegans, E. 

 hamata, and possibly S. lyra. 



3. Cool water species, temperature 19 ?0 to 9?5 This group 

 includes 8. decipicns and Spadella ccphaloptera. 



4. Warm water species, temperature 34?0 to 15?0. This 

 group includes the remaining species, iS". enflata, S. puhhra, 8. 

 neglecta, S. regidaris, 8. bedoti, 8. ferox. 8. minima, 8. tenuis, 

 8. gazelle, 8. hispida, and 8padella draco. 



It is to be noted that these groups are not sharply defined. 

 8. lyra, for instance, while placed in the second group, might be 

 placed in the first, although it has a greater tendency than the 

 others to confine itself to cold water. 8. plankfo)tis, again is 

 eurythermal regarding vertical distribution, but seems otherwise 

 to be confined to temperate and tropical regions. It is quite 

 possible that, after more extensive collecting with closing nets in 

 the various latitudes, many of the species will be discovered to 

 be eurythermal, with regard to vertical distribution, latitude, or 

 both. 



