176 FISHES. 



Similar changes take place in a number of other fishes, 

 and in many cases the young are so different that they were 

 described as distinct genera : thus Priacantichthys has proved 

 to be the young of Serranus, Rhynchichthys that of Holocen- 

 trtcm, Cejphalacanthus of Dactylopterus, Dicrotus of Thyrsites, 

 Naiiclerus of Naucrates, Porthmeus of Chorinemus, Zampugus 

 of Coryphcena, Acronurus of Acanthurus, Keris of Naseus, 

 Porohronchus of Fierasfcr, Couchia of Motella, Stomiasunculus 

 of Stomias, etc. 



The fins are most frequently subject to changes ; but, 

 whilst in some fishes parts of them are prolonged into fila- 

 ments with age, in others the filaments exist during the early 

 life-periods only ; whilst in some a part of the dorsal or the 

 ventral fins is normally developed in the young only, in 

 others those very parts are peculiar to the mature age. The 

 integuments are similarly altered : in some species the young 

 only has asperities on the skin, in others the young are 

 smooth and the old have a tubercular skin ; in some the 

 young only have a hard bony head ; in others (some Silu- 

 roids) the osseous carapace of the head and neck, as it appears 

 in the adult, is more or less covered with soft skin whilst 

 the fish is young. 



In not a few fishes the external chancres are in relation 

 to the sexual development {Callionymiis, many Labyrinthici, 

 Cyprinodonts). These secondary sexual differences show them- 

 selves in the male individual, only when it commences to enter 

 upon his sexual functions, and it may require two or more 

 seasons before its external characteristics are fully develoj)ed. 

 Immature males do not differ externally from the old female. 

 The male secondary sexual characters consist principally in 

 the prolongation of some of the fin-rays, or of entire fins ; and 

 in Salmonidm in the greater development of the jaw-bones. 

 The coloration of the male is in many fishes much brighter 

 and more variegated than that of the female, but in com- 



