No. 465.] STUDIES OF MYXINOIDS. 629 
University, quoted by Jordan and Evermann states that in fifty- 
four specimens which he counted, forty-one had twelve gills on 
each side, twelve had eleven gills, and one had thirteen gills. 
He states also that he occasionally found one with ten or four- 
teen on each side, but that the normal number was twelve. 
Worked out in percentages, this would read : — 
Individuals with 12 gills 75.0 %. 
ex 11.8 222% 
m “ 13 « 1.8 ob. 
When tested by the examination of larger numbers of indi- 
viduals, however, these figures undergo considerable modifica- 
tion, and a new factor enters in, f. e., fish that have a different 
number of gill slits on the two sides. The following table is 
given by Dr. Ayers in his paper published in 1894 :— 
101 individuals had 11 gill wey on both sides ; 
26 moa ees * one side and 
12 44 ow — s other ; 
208 « “ I2 * * & both sides; 
T “ “ 2 * & & one side and 
Fi * " P Ihe other; 
8 L “34 * «* e both sides. 
354 total number of individuals counted. 
Worked out in percentages this reads : — 
Individuals with 11 slits on each side . . . 2857 
u i an 
iz. = " theothr . ‘ 293% 
“ u 449 “© © ehade ' ^ . 58.7% 
t « I2 « * one # and 
HE . . -. 31% 
e « yg *" * eachside . ‘ | 22% 
These figures, as will be seen, reduce the percentage of those 
having twelve slits on each side by one third, add very nearly 
one third to the percent of those with eleven slits on each side, 
increase slightly the percentage of those with thirteen on each 
side, and introduce the two intermediate forms, those with 
