FIS 



sible to generalise them. In general the approach 

 toward the shore of fishes for the purpose of spawning, 

 is an operation of the greatest possible value to man. 

 At the time when the roes and milts are coming to 

 maturity, all the energies of the fish appear to be 

 excited to a more than ordinary degree ; so that at 

 this time, and up almost to the period when the spawn 

 is ripe for being deposited, the fish are in the best 

 condition for the table ; and thus they may be said to 

 come on the shores almost on purpose to be caught. 

 The eggs of different fishes vary much in colour ; but 

 those of all the species in the present division, agree 

 in being perfectly -globular. None of them have 

 shell?, but they are enveloped in a membranous integu- 

 ment. This integument is more or less firm according 

 to the species. The yolk, instead of occupying the 

 centre, as in the eggs of birds, is placed laterally, and 

 is surrounded by the glaire or albuminous matter. 

 Betsveen the yolk and the glaire is situated the 

 gerrn or embryo. The germ becomes ready for 

 exclusion at very different periods, according to the 

 species. Thus the egg of the carp is said to be 

 perfected in the course of three weeks, while that of 

 the salmon requires as many months. But in the eggs 

 of the same species, a great deal depends on the tem- 

 perature to which they are exposed. In the same 

 pond, those eggs are soonest hatched which have 

 been deposited in the shallowest water. As the em- 

 bryo is developed, the heart first appears, afterwards 

 the spine, eyes, and tail. The organs of motion are 

 evolved in the following order. The pectoral fins 

 first make their appearance, and afterwards those of 

 the tail ; the dorsal fins follow, and then the ventral 

 and anal fins. In fishes, such as the salmon, which 

 bury their spawn under the gravel of rivers and 

 brooks, the appearance of the young at first is very 

 singular, as they come up through the covering, while 

 the lower part of the body remains attached to the 

 remainder of the egg below. 



In fishes which hatch their young, the eggs are 

 fecundated internally ; but observations have been 

 made on comparatively few fishes of this division, and 

 therefore our information respecting them is com- 

 paratively vague. The sharks and rays are the ones 

 to which most attention has been paid ; and the fol- 

 lowing remarks will show in outline the progress of 

 the young in these. The females have two ovaries, 

 or egg vessels, situated at the sides of the spine, and 

 containing eggs in different stages of forwardness. 

 An oviduct proceeds from each of these, the an- 

 terior extremities of which are united to the dia- 

 phragm and spine. Internally, these ducts are covered 

 with glandular papillae, and pass through a large 

 glandular body. After passing this body, they 

 dilute into a large sac. When the ova pass into 

 the oviduct they are carried to this glandular body, 

 which is supposed to secrete the glaire or albu- 

 minous part, and afterwards conveyed to the 

 uterus, where they receive the shell. At what 

 period the egg becomes impregnated, or in what 

 manner the operation is performed, are questions to 

 which no satisfactory answers can be returned. The 

 eggs are of a quadrangular form, with processes at 

 the four corners ; they are called sea mice by some, 

 but by fishermen they are called skate-purse, or 

 shark-purse. The shell has a horny consistence, 

 and may often be observed, at certain seasons, among 

 the rejectamenta which the sea casts, as being no 

 longer useful in its economy. When the young fish 

 have been perfected in the uterus, where they derive 



H. 4*1 



.heir nourishment exclusively from the egg, and not 

 "rom the mother, they are ejected through the open- 

 ngs of each uterus, at the sides of the cloaca, and 

 ipon escaping from the shell, enjoy immediately an 

 ndependent existence, and begin to search after 'new 

 nourishment. 



The individual broods, or shoals of production, in 

 fishes of this description, are not nearly so numerous 

 as those of the oviparous fishes, though from the dif- 

 ferent stages of growth, at which the eggs are contem- 

 porneously found in the females, it is probable that 

 the period of production lasts considerably longer. 

 Such fishes have not the same necessity for migrating 

 in search of proper breeding grounds as the others, 

 and therefore the whole sea is comparatively free to 

 them at all times in proportion to their habits. It 

 farther appears that they are not so much exhausted 

 by the labour of reproduction, and thus their flesh 

 does not get so much out of season as that of the 

 others. This may also, in conjunction with the soft- 

 ness of the bones, which never know old age (see 

 CHONDROPTEHYGII), contribute to the large size, 

 inexhaustible strength, and long life of these fishes. 



In the sea, it does not appear that there are any 

 hybrids among fishes, any more than there are among 

 land animals in^a state of wild nature ; but the case 

 is said to be different in ponds, in which carp and trout 

 are sometimes said to blend their several qualities. 

 This point, though one of some interest it' fish were 

 cultivated as they ought to be, is one which is involved 

 in very considerable obscurity. 



The following table, the result of useful observa- 

 tions which are extracted from the Philosophical 

 Transactions for 1767, will give some idea of the rela- 

 tive fertility of several species of oviparous fishes : 



From this table it appears that there is no constant 

 proportion between the weight of the fish and the 

 number of eggs, or the weight of the roe. We have 

 also no means of ascertaining any thing with respect 

 to the relation between the size of the present fish 

 and that of their progeny ; as, for instance, we are 

 unable to tell whether the fry that are produced from 

 the roe of a small fish, are equal to, or greater or less 

 than those produced by the roe of a larger fish of the 

 same species, or the same age. We have also no 

 means of ascertaining what proportion there may be 

 between the eggs that are deposited and the number 

 of fish that are hatched, and between the number 

 that come to maturity. The eggs are eagerly sought 

 after by other fishes, by aquatic birds and reptiles. 

 In the young state, they are pursued even by their 

 own species, as well as by beings belonging to other 

 classes. But for the numbers of eggs thus produced, 

 the very race of fishes would soon be extinguished 

 by enemies while young ; and we may add, that the 

 diminution of the number of eggs would cut off' a large 

 supply of food, and destroy that dependence which 



