CHAETOGKA.THA COLLECTED BY STEAMER ALBATROSS. 



273 



Table 19 shows (1) that in every case the mean number of both 

 anterior and posterior teeth in Philippine specimens exceeds that in 

 San Diego specimens, and (2) that the magnitude of the excess is 

 between 5 and 20 times the corresponding probable error. That this 

 excess is not merely an expression of the larger size of the Philippine 

 specimens is evident, for the counts were made on specimens of 

 Philippine Sagitta enjiata between 10 and 21 mm. in length and on 

 San Diego specimens between 10 and 25 mm.; on Philippine S. 

 neglecta between 6 and 8 mm., and on San Diego specimens between 

 8 and 13 mm. ; on Philippine S. serratodentata between 7 and 11 mm., 

 and on San Diego specimens between 10 and 17 mm.; and on Philip- 

 pine S. planktonis between 13 and 27 mm., and on San Diego speci- 

 mens between 17 and 26 mm. Obviously, some differential influence 

 is at work in the two regions causing an excess of teeth in the Philip- 

 pine fauna, or a deficiency in the San Diego fauna. 



Unfortunately, a similar comparison of Philippine chaetognatha 

 with those from other regions of the Pacific is impossible, owing to 

 the fact that no one except Fowler (1906) has published a series of 

 tooth counts, and he has not kept the individual counts distinct. 

 The range of variation, however, in the Siboga material is much the 

 same as that in Philippine specimens. This is pointed out in the 

 foregoing pages for every species common to the two regions, but 

 these data are brought together and amplified in Table 20 : 



Table 20. — Comparison of number of anterior and posterior teeth in Philippine species 

 and those from the Siboga region. 



SAGITTA ENFLATA. 



SAGITTA NEGLECTA. 



SAGITTA SERRATODENTATA. 



