No. 465.] STUDIES OF MYXINOIDS. 633 
either a fixed or a normal number of gills, this could only mean 
that this particular animal was a freak. But where we have 
variations of the species in which the number of gills ranges 
from thirteen to seven, and one variation (that from California), 
in which no number can be considered either normal or fixed, 
and where the last gill on one side is found to be either rudi- 
mentary or missing, there is certainly an indication of a ten- 
dency to the suppression of the gills. Moreover, in the last 
case the rudimentary and the missing gill are both in an unusual 
place (the cephalic instead of the caudal end of the line). Still 
another variant bears out this view. This variant was one of the 
even-numbered group, with twelve gills on each side. On open- 
ing the thoracic cavity, it was found that while the fish had 
twelve normal gills on the right side, on the left the first was 
missing, and the second rudimentary. As in the case last men- 
tioned, the external aperture of the missing gill led into a cu/ de 
sac and there was no pharyngeal opening. In this fish there 
was no external mark to indicate the slightest abnormality 
within, which raises the question : What percentage of abnor- 
mality would be found if careful dissection were made of the 
gill regions of a large number of individuals? 
There is no particular size in which these variations occur. In 
the last one given, the fish was only eleven and one half inches 
long ; in the one preceding, twenty-one and one half inches long; 
the others varied between these two. It would be interesting 
if some young hagfish with an uneven number of gills, particu- 
larly individuals where the distance between the ductus and the 
nearest gill is less than normal, could be kept under observation 
for a number of years, to see if any changes occur during the 
life of the individual, or if these variations are fixed during 
larval growth and remain fixed during adult life. It would also 
be of great value in this connection if the other varieties of 
hagfish could be more carefully studied, to determine if the vari- 
ation in the number of gills is as great as that of the California 
hag, and if so, when the variations occur. It should also be 
determined whether the number is more constant among the 
groups having a small number of gills. 
