548 
surface, and fertilization from other species occurred prior to or 
during the time they were subsiding, the possibility of cross- 
breeding would be restricted to such taking place with those of 
other forms whose eggs similarly sink. In the same way the 
milt of the male, if ejected near the surface, may, while sub- 
siding, occasionally come in contact with the eggs of forms 
which normally float. In mixogamous forms, where the males 
and females congregate together for breeding purposes, and 
large tracts of the ocean are discoloured by the presence of 
their eggs and milt, it does not seem very difficult to suppose 
that a ripe fish of another species or genus might accidentally 
be present and hybridization occur.; while there are forms, 
as the mackerel, Scomber scomber, cod, Gadus morhua, and most 
of our flat fishes, or Plewronectide, in which the eggs float, or 
have their specific gravity so nearly similar to that of the sea 
that it requires the agitation of the waves to prevent their 
subsiding. Some marine fish, as blennies, attach their eggs to 
shells or other substances, but these cases will furnish me with 
no instances of hybridization. 
Among the fish which reside in fresh waters, or seek a fresh 
water locality in which to deposit their eggs, we have very few 
that have floating ova: shad, Clupea alosa and C. finta being 
possibly the exceptions. The Salmonide make a nest or redd 
in the gravel at the bottom of a stream, and subsequently leave 
their eggs and young to care for themselves; while among 
the perches and carps some deposit their ova in stringy bands. 
But while it is evident that eggs may be carried by waves, 
currents, or winds to where the milt of another species might 
be present, or milt may be similarly washed away from the 
circle wherein the species has deposited its eggs, still there are 
certain causes in existence which are detrimental to hybridiza- 
tion when in a state of nature. For the mode in which 
fertilization takes place is, that the milt or spermatozoa, of the 
male is brought into contact in the water with the ova or eggs 
of the female, and obtains access through a small orifice 
termed the micropyle into the interior of the ovum. It must, 
however, be evident that simple as this process would be between 
