BULLETIN OF THE UNITED STATES FISH COMMISSION. 59 
! operation of spawning over fully two months.” The result of this ar- 
rangement is that some of the American codfish begin to spawn in Sep- 
tember, and some continue as late as June. The cod in our seas do not 
follow the same habit, though their spawning period extends on each 
side of the beginning of April. In the same way the period during 
which the eggs of the various kinds of skates are deposited is consider- 
ably lengthened. 
On the other hand, such marine fishes as the lumpsucker ( Gyclopterus 
lumpus ?) and bimaculated sucker, the salmon, trout, and most fresh- 
water fishes seem to deposit their eggs within the limited period of a 
day or two, and consequently the development of the masses of eggs 
in the ovaries is more nearly simultaneous. 
In general form the eggs of ordinary fishes are circular. On deposi- 
tion they are usually invested by a single layer (zona radiata ), though 
in some, as in the herring, there is another, namely, the vitelline mem- 
brane, which lies outside the former. The great mass of the egg is 
formed by the oval spherules of the food-yelk, which are separated by 
protoplasmic bands. Hear one of the poles the protoplasm usually 
forms a lenticular area, the germinal disk or germinal area, and the 
smaller yelk-spherules in this region differ in character from those of 
the general mass of the egg. During development the eggs show par- 
tial segmentation, the process being chiefly confined to the germinal 
area. 
While the circular form as just described is characteristic of the eggs * 
of most fishes, we have a few marine types which deviate from the gen- 
eral rule, such as the glutinous hag (Myxine glutinosa ), with its ovoid 
and fringed eggs; the goby, with its fusiform ova ; the gar pike, saury 
pike, and flying-fish, which have long filaments attached to their eggs, 
probably for the purpose of fixing them to floating structures of any 
kind. Among other interesting types are the large eggs of the stickle- 
back and the salmon tribe, and the almost microscopic eggs of the eel. 
The large ova of the salmon and trout are surpassed, however, by those 
of the siluroid genus Arius, found both in the Old World and the Hew 
(Ceylon and Guiana), the eggs being somewhat larger than a pea (5 to 
10 mm .) ; but this is not the only remarkable feature in these fishes; for 
as Drs. Gunther and Wyman and Professor Turner have shown, the 
large eggs are carried by the male in his mouth and gill-chamber until 
hatched, the small and almost granular palatine teeth making this pos- 
sible without injury to the ova. He thus acts the part of a “ dry- 
nurse,” as also does the male pipe-fish ( Syngnathus ) and the sea-horse 
(Hippocampus), the eggs being borne by the male in a pouch on the un- 
der surface. In another siluroid fish (Aspredo) from Guiana, the re- 
markable exception occurs of a female fish interesting itself in the care 
of its young. The skin on the under surface becomes soft and spongy, 
and the eggs, which are deposited on the ground, adhere by simple 
pressure of the body over them, very much after the arrangement in the 
