612 ANATOMY OF VERTEBRATES. 



slender tlian that of the mature fish, or the height of the body is 

 less in comjiarison with its length. The eye ceases to grow long 

 before the individual has attained its full size ; so that old fishes 

 have comjiaratively smaller eyes than young ones. The form of 

 Fishes is altered by changes in the shape of fins, by the develope- 

 ment or by the loss of spines belonging to the opercular apparatus 

 or to the fins ; as in the following examples. 



' a. Some of the fin-rays are prolonged with age into long 

 filaments : species of Antldas, Pagrus, Ephijipus, CalUonymus. 



' h. Some of the fin-rays are prolonged in young individuals, 

 Ijut the filaments are worn off with age : Lophius, Echeneis, 

 Tracliynotus. 



' c. Cephalacantlius is merely the young of Dactylopterus ; 

 the pectoral fins are short in the young, and become with 

 age so long as to serve for an organ of flying in the adult 

 (JDuctyloptcrus). 



' d. In some species of Thyrsites and Gempylus the ventral fin 

 is reduced to a very small spine, which in the young is very 

 long, nearly half as long as the head. Sometimes the young 

 has ventral fins, whilst they are entirely absent in the adult: 

 Stromatcus. 



' e. The young of almost all the Carangidoi have the pra>oper- 

 culum armed, like a Percoid : this bone is entirely smooth in the 

 mature fishes. The same in Labrus. 



'/. Some fish have no visible, or but a rudimentary, spinous 

 dorsal fin ; this fin is very distinct in the young : Brama, Platax, 

 Stromateus. 



' g. Large prominences of the skin are developed, which arc 

 absent in the young : Cyclopterus. 



' h. Llany of the well-armed Siluroids have the osseous carapace 

 on the head and neck more or less covered with skin in early 

 age : the dorsal and pectoral spines are more feeble in the young 

 than in the old.' ' 



There arc few fields of Natural History that return more mate- 

 rial reward for scientific labour than that relating to the generation 

 and growth of Fishes. The mercantile value of the Salmon, 

 and the necessity for basing laws that arc to operate in its 

 preservation upon a knowledge of its natural history, have led to 

 interesting observations on its growth and migrations. 



Mr. Shaw,^ observing ova spawned on January lOtli, no- 

 ticed dark eye-specks and some movement of the embryo in 



' For tlio above examples I am imlebtcd to my colleague, Ur. A. Giiiitlier. 



'' cxxiv, 



