DEVELOMIENT OF FISHES. 303 



fishes is tlie transposition of the periods of extrication and exclusion : 

 in the Ovipara the generative product or ovum quits the parent 

 before the embryo extricates itself from the egg : in the Ovo-vivipara 

 the embryo escapes from the egg before it quits the parent : the 

 young Blennies tarry three months in utero, from September to 

 January, after extrication from the chorion. The great difterence 

 between viviparous fishes and mammals is, that the former rupture 

 the chorion long before they are born, even in the Sharks where 

 there is a kind of pseudo-placental attachment : in the fcjctal mammal 

 birth and exclusion are commonly coincident. 



Groivth. — There are few fields of Natural History that have been 

 less cultivated, or would better reward the scientific labourer, than 

 that extensive and varied one relating to the generation of fishes. 



The mercantile value of the Salmon, and the necessity for basing 

 laws that are to operate in its preservation, upon a knowledge 

 of its natural history, have led to some very interesting observ- 

 ations ; the following are the chief results of those recorded by 

 Mr. John Shaw in the Transactions of the Royal Society of Edin- 

 burgh, for 1840. 



The embx'yo fish, developed from the ova spawned on the lOtli 

 January, were conspicuous by the two dark ej^e-specks and the 

 vascular vitelline sac, and presented some appearance of animation 

 in the ovum, on February 26th, that is, forty-eight days after being 

 deposited ; and on 8th April, or ninety days after impregnation of 

 the ova, the young were excluded. The head is large in proportion 

 to the body, which measures f ths of an inch in length ; the vitellicle 

 is f ths of an inch in length, and resembles a light red currant ; 

 the tail is margined like that of the tadpole, with a continuous fin 

 running from the dorsal above to the anal beneath. The vitelline 

 sac and its contents were absorbed by the 30th May, or in about 

 fifty days, until which time the young fish did not leave the gravel. 

 This quiescent state in their place of concealment, from the period 

 of exclusion to the absorption of the yolk, seems to be common 

 to osseous fishes ; but the time varies in different fishes, it is much 

 shorter in the Tench, for example, than in the Salmon. AVhen the 

 young of this fish emerge, the terminal fringe-like fin begins to 

 divide itself into the dorsal, adipose, caudal and anal fins ; and the 

 transverse bars on the side of the body make their appearance. At 

 this period, the young Salmon measures an inch in length, and is 

 very active, and continues in the shallows of its native stream till 

 the following spring, when it has attained the length of from tliree 

 to four inches, and is called the " May-parr : " they now descend into 

 deeper parts of the river, and are believed by Mi-. Shaw to remain 

 there over the second winter. In April, the caudal, pectoral, and 



