GILL] LIFE HISTORIES OF TOADFISHES 399 
comes, in this instance, at least, has a great deal to do in determining 
the direction of the axis of the body of the future embryo. This 
position of the young fishes is maintained as long as they are 
attached.” 
Miss Wallace found (1898) that “not until the fourth or fifth 
day after fertilization does a distinct axial thickening appear.” 
The period of incubation was supposed by Ryder to be about 15 
to 20 days, but by him “the exact duration of its development was 
not determined.” ‘While the embryos are still adherent, the tail 
_1s not kept constantly vibrating, but the pectoral fins are kept in 
motion so as to keep up currents of water and effect the constant 
change of the latter, needful for the respiration of the embryos.” 
Meanwhile the fins gradually approximate to the adult form, the 
body grows and the yolk becomes absorbed, and when finally free 
an unmistakable toadfish has been developed. By the time it has 
reached a third of an inch (8 mm.) in length, it has assumed the 
form of maturity and the fins are fairly developed although the 
heterocercal tail and embryonic fin folds connected with it are still 
retained ; according to A. Agassiz (1882), who has described such 
a stage, “the whole fish was dotted with small pigment spots, 
with a few larger cells scattered irregularly over the surface; the 
pectorals were similarly colored. The general tint of body and fin 
was gray, with blackish and yellowish pigment cells.” 
The transition from egg to fish takes a rather long time compared 
with most fishes. Ryder judged that the fixed condition of the egg 
and embryo lasts for at least three or four weeks but “the egg 
membrane is ruptured in about half that time.” 
The subsequent development also presents some exceptional fea- 
tures. “ The development, as it advances, enables the young embryo 
within the egg membrane to finally rupture the latter immediately 
over the back, which looks down and away from the surface to 
which the egg is attached. When the zona or egg-membrane is 
ruptured, the young fish is, however, not set free at once, as in the 
case of other adhesive ova, but remains firmly glued to the inside 
of the zona over a part of the ventral surface of the yolk-bag.” 
The care of the father, it has been claimed, does not cease with 
the liberation of the young from the eggs. According to Stearns, 
“when its young have been hatched, the older fish seem to guard 
them and teach them the devices of securing food in much the same 
'Ryder’s generalization appears to be rather more categorical than the 
facts warrant. At least a photograph taken from life by Dr. E. W. Gudger 
shows several deviations of larve from a uniform trend of direction. 
