108 University of California Puhlications in Zoology. [Vol.8 



temperate and tropical regions. To test this statement I tabu- 

 lated all accessible data, and discovered that it rested mainly on 

 isolated observations and collections made with open vertical 

 nets. 



Data depending on collections made with these nets are of 

 questionable value. This has been noted by Agassiz, Fowler, and 

 others. In discussing the methods of collecting employed by 

 the "Challenger" expedition Agassiz (1888, p. 35) says: "The 

 old practice was employed of dragging for animal forms at inter- 

 mediate depths by means of a tow-net, which, during the several 

 operations of lowering, dragging, and hauling back remained 

 open ; this cannot be regarded as afifording acceptable evidence 

 of the habitat of such specimens as were obtained." Again 

 FoM'ler (1905, p. 81), after pointing out that »S'. furcaia was 

 obtained abundantly in closing nets from 150 to 50 fathoms, and 

 that below 200 to 100 fathoms the closing net failed to obtain 

 the species, says: "The specimens recorded in open nets below 

 100 fathoms were therefore probably caught in the vertical 

 journey upward ; an instance of the deceptiveness of the method 

 of open nets." To illustrate further the inadequacy of these nets 

 I have selected the following instances from our data concerning 

 the vertical distribution of the San Diego Chaetognatha. 



1. During a period of four years 1-1 open net hauls were 

 made below 110 fathoms, 15 from a variety of depths between 110 

 and 25 fathoms, and 13 from above 25 fathoms. Of the 1-4 hauls 

 from below 110 fathoms 12 contained a total of 668 specimens 

 of 8. serratodentata. Of the hauls from between 110 and 25 

 fathoms, one from 75 fathoms contained 6, and one from 25 

 fathoms 2 specimens of the same species, while in the 13 hauls 

 from above 25 fathoms no specimen.s were found. 



2. During a period of four. years 8. lyra was obtained in 10 

 out of 21 open net hauls from or below 75 fathoms. During the 

 same period 20 open net hauls were made from above 75 fathoms 

 which failed to obtain the species. 



Dare we conclude that *S'. serratodentata does not exist above 

 25 fathoms, or that S. lyra does not exist above 75 fathoms? 

 Obviously such a conclusion is based on the absence of the species 



