BATHYPELAGIC SQUID BATHYTEUTHIS 81 



30 40 50 60 70 75 



ML 



Figure 19. — Bathyteuthis bacidifera and B. ahyssicola: a, gill width vs. mantle length; 

 b, gill length vs. mantle length. 



3. Gill width 



The plots of gill width against mantle length (hg. 195) indicate a 

 distinct separation between the two species. The points for eastern 

 Pacific ahyssicola lie just above those for Antarctic specimens, but, 

 still, these gills are distinctly narrower than those of hacklifera. 



The means of the gill width to mantle length indices for ahyssicola^ 

 plotted on figure 20i^, lie between 5.5% and 7.4%, but \\\q mean index 

 for hacidifera is 12.4%. Altlioiigh the gills of eastern Pacific ahyssicola 

 tend to be slightly wider than those of other specimens, the difference 

 is not nearly so great as between the populations of ahyssicola and of 

 hacidifera. The gills of hacidifera average nearly 2.3 times wider than 

 the gills of Antarctic ahyssicola and 1.7 times wider than eastern Paci- 

 fic ahyssicola. Therefore, gill width is significantly greater in hacidi- 

 fera than in ahyssicola. 



4. Gill width : gill length index 



Perhaps a better expression of actual gill size is the index of gill 

 width to gill length. Figure 20(? plots the average values for the popu- 

 lations of Bathyteuthis; the data are summarized in Table VI. B. 

 hacidifera has a mean gill-width to gill-length index that is consider- 

 ably greater than that for ahyssicola. That is, the width of any sized 

 gill of hacidifera will be about one-fourth of its length, but in ahys- 

 sicola it will be only about one-sixth of the gill length. 



