720 PISCES. 
The sexes in fishes are, in the greater portion, in separate individuals. 
The ova are generally impregnated by the male after extrusion, and the 
young are developed without the care of the parent. The male is known, 
besides other distinctions, by the presence of the testes, or milt, and the 
females by the ovary, or roe, which both occupy the same relative place in 
the body of the animals. Those are said to be viviparous, in which the ova 
are matured, and the young developed before extrusion. In the develope- 
ment of the embryo, the heart first appears, afterwards the spine, eyes, and 
tail. Of the organs of motion, the pectoral fins first appear, followed in suc- 
cession by the caudal, dorsal, and anal fins. Among the oviparous fishes, 
hermaphroditism was long considered as a rare and accidental circum- 
stance. Baster noticed this occurrence in the whiting, Duhamel in the 
carp; Haller gave his testimony to facts of the same nature; and Pallas 
believed that the genus Syngnathus had no males. Lastly, Sir Everard 
Home, in the Philosophical Transactions for 1815, states the same fact re- 
garding the lampern or pride, and the Gastrobranchus cecus of Bloch. 
The amazing reproductive powers of fishes are well known. In the ovary 
of the cod in December, were formed three millions six hundred and eighty- 
six thousand seven hundred and sixty ova; in the flounder in March, one 
million three hundred and fifty-seven thousand and four hundred; in the 
herring in October, thirty-six thousand nine hundred and sixty; and in the 
tench, three hundred and eighty-three thousand two hundred and fifty-two. 
And Bloch relates, as the result of an experiment, regarding the productive 
power of the carp, that, ina pond of seven acres, in which were placed four 
males and three females, the increase in one year was one hundred and ten 
thousand young carp, a number too great for the size of the pond and the neces- 
sary supply of food. But this astonishing capability of increase is modified by 
a thousand circumstances, which regulate the number produced to the supply 
of food. Myriads of these ova form the food of different species; and myri- 
ads more of the young may be supposed to be destroyed in an element 
where almost all are destined to become the prey of one another. Notwith- 
standing these deductions, however, the importance of this class as an 
object of commerce, and as a supply of food, holds out an inexhaustible field 
for the enterprise of nations whose territories approach the sea. Of the 
migrations of fishes, and the causes which prompt these annual influxes of 
certain fishes, on certain coasts, little is with certainty known. Probably 
they are regulated by the same causes which influence the migrations of 
birds, to find food and proper places for reproduction ; and the same instinc- 
tive impulse which induces the salmon, at certain seasons, to ascend rivers, 
may bring myriads of fishes to the shores for a similar purpose Little is 
known with regard to the comparative age of fishes. The carp has been 
known to reach two hundred years, and the pike to two hundred and sixty , 
and if whales be found of less size now than in former ages, when their 
