178 The Cyclostomes, or Lampreys 
observation of individuals. Of the specimens that run up 
early in the season, about four-fifths are males. Thus the 
males do not exactly precede the females, because we have 
found the latter sex represented in the stream as early in the 
season as the former, but in the earlier part of the season the 
number of the males certainly greatly predominates. This pro- 
portion of males gradually decreases, until in the middle of 
the spawning season the sexes are about equally represented, 
and toward the latter part of the season the females continue 
to come until they in turn show the greater numbers. Thus 
it appears very evident in general that the reproductive in- 
stinct impels the most of the males to seek the spawning ground 
before the most of the females do. However, it should be said 
that neither the males nor the females show all of the entirely 
sexually mature features when they first run up-stream in the 
beginning of the season, but later they are perfectly mature 
and ‘ripe’ in every regard when they first appear in the stream. 
When they migrate, they stop at the site that seems to suit their 
fancy, many stopping near the lake, others pushing on four 
or five miles farther up-stream. We have noted, however, 
that later in the season the lower courses become more crowded, 
showing that the late comers do not attempt to push up-stream 
as far as those that came earlier. Also it thus follows, from 
what was just said about late-running females, that in the latter 
part of the season the lower spawning beds are especially crowded 
with females. In fact, during the early part of the month of 
June we have found, not more than half a mile above the lowest 
spawning bed, as many as five females on a spawning nest with 
but one male; and in that immediate vicinity many nests 
indeed were found at that time with two or three females and 
but one male. 
‘Having arrived at a shoal which seems to present suitable 
conditions for a spawning nest, the individual or pair commences 
at once to move stones with its mouth from the centre to the 
margin of an area one or two feet in diameter. When many 
stones are thus placed, especially at the upper edge, and they 
are cleaned quite free of sediment and alge, both by being 
moved and by being fanned with the tail, and when the proper 
condition of sand is found in the bottom of the basin thus formed, 
