io8 The American Naturalist. [March, 
most interesting of the species. An account of it will serve for 
all the others. As is well known, the egg-bearing lamellae are 
broad sheets which are suspended from the roof of the ovary ; 
there are usually thi'ee of these sheets in each half of the ovary. 
The eggs are very small (.2 mm.) as compared with the eggs of 
other fishes : they protrude from the lamellae much as other fish 
ova do and they seem to be surrounded by a more transpar- 
ent area. I have seen the eggs of several species but for lack 
of proper facilities to study the material collected a more de- 
tailed description cannot be given at present. The eggs of 
Micrometrus aggregatiis have the yolk collected in spherical 
masses, and there seems to be no oil globule, while the eggs of 
Ditrema jacksoni have from one to three oil globules. Whether 
the eggs are fertilized before they are freed from the lamellae, 
I cannot state al: present ; long before hatching, the eggs are 
found lying in the folds of the ovary. The eye is much less 
conspicuous than in other fish embryos, and the hypertrophied 
hind gut is developed before hatching. In larvae in which the 
mouth w^as apparently not yet formed, the vent was open and 
the vigorous peristaltic action which was confined to the hind 
gut began at the vent and traveled forward ; this would seem 
to make it probable that food is taken in through the vent in 
the earliest stages of the larval existence. A structure whose 
significance has not yet been determined is found in larvae less 
than half an inch long. It consists of a spirally twisted, opaque 
white substance lying free in the hind gut ; it terminates pos- 
teriorly in a knob ; its anterior connection has not been traced. 
During the peristaltic movement mentioned, this spiral moves 
freely, and in several instances it was entirely withdrawn from 
the hind gut, the knob at its posterior extremity seeming to 
form a partial plug at the anterior end of the posterior intes 
The first indications of the peculiar prolongations of the ver- 
tical fins was noticed in larvae an inch long; all the fins were 
well developed and the interradial membranes projected as 
short, broad flaps beyond the tips of the rays. 
The Herring, Clupea mirabilis, enters the bay of San Diego 
