246 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Distribution. — S. hexaptera was collected from 26, or 57 per cent, of 

 those stations at which chaetognaths were captured. Of these, 8 

 were rnesoplanktonic, while 13, or one-half, were surface stations. 

 From the 8 rnesoplanktonic stations a total of only 70, or an average 

 of 9 to each station, was obtained, while the 18 epiplanktonic stations 

 yielded 642, or an average of 36 per station, and the 13 surface sta- 

 tions yielded 491, or an average of 38 per station. It is evident, 

 therefore, that S. hexaptera occurs typically in the upper epiplankton 

 of the Philippine region. 



S. hexaptera, often confused with S. elegans and with the large 

 variety (S. maxima) of S. lyra, is a eury thermal, nearly cosmopolitan 

 species found typically in the lower epiplankton and mesoplankton 

 of the arctic, sub-arctic, north temperate, tropical, and south tropical 

 Atlantic, the south temperate and tropical Indo-Australian, and the 

 north temperate and sub-antarctic Pacific oceans. Its northern and 

 southern limits of distribution are 74° north and 28° south, while 

 the extremes of temperature recorded in connection with its capture 

 are 29° C. and 6° C. A statement frequently encountered in the 

 literature is that surface Chaetognatha of the arctic seas would be 

 found, if at all, in the mesoplankton of temperate and tropical 

 regions, the implication being that temperature plays the all- 

 important part in delimiting the vertical distribution of a species. 

 Obviously, the typical occurrence of S. hexaptera in the upper epi- 

 plankton during the Philippine expedition contradicts this statement, 

 which contradiction is further supported by Ritter-Zahony (1911, 

 p. 54), who says: "Es gibt keinen einzigen verbiirgten Fundort del- 

 is', hexaptera aus dem Epiplankton der Meere nordlich von 40° N." 

 Rather do the facts point in quite the opposite direction, that is 

 that surface S. hexaptera of tropical and sub-tropical regions are 

 found, if at all, in the lower epiplankton and mesoplankton of arctic 

 and sub-arctic regions. However, until consistency of identifica- 

 tion of the species obtained during the various expeditions is attained, 

 and until the vertical distribution of the species in diversified regions 

 is critically studied, no conclusion as to the, part played by tempera- 

 ture or any other environmental influence, in controlling its distri- 

 bution throughout the world, is justified. 



The northernmost and westernmost record of its capture during 

 the Philippine expedition is 21° 31' north and 117° 53' east in the 

 China Sea, off Hongkong. Its southernmost record is 5° 36M south 

 and 122° 7'. 6 east, in Buton Strait; and its easternmost record is 

 127° 44' east and 1° 3' south, south of Patiente Strait. The largest 

 number (153 + ) was taken August 11, 1909, at 7.49 in the evening, 

 from the surface between Siquijor and Bohol Islands, at 9° 27'. 5 

 north and 123° 38' east. Other species obtained at the same station 

 are: 169 S. enfiata, 128 S. pulchra, 50 S.ferox, and 14 8, bedoti. 



