SEXUAL DIFFERENCES. 177 



paratively few permanent (as in some Callionymus, Zahrus 

 mixtus) ; generally it is acquired immediately before and 

 during the season of propagation only, and lost afterwards. 

 Another periodical change in the integuments, also due to 

 sexual influence and peculiar to the male, is the excrescence 

 of wart-like tubercles on the skin of many CypriTwids ; they 

 are developed chiefly on the head, but sometimes extend over 

 the whole body and all the fins. 



With regard to size, it appears that in all Teleosteous fishes 

 the female is larger than the male ; in many Cyprinodonts the 

 male may be only one-sixth or even less of the bulk of the 

 female. The observations on the relative size of the sexes 

 are few in Pala3ichthyes, but such as have been made tend to 

 show that, if a difference exists at all, the male is generally 

 the larger (Lepidosteus). In the Eays (Baja) the sexes, after 

 they have attained maturity, differ in the development of 

 dermal spines and the form of the teeth, the female being 

 frequently much rougher than the male. There is much 

 variation in this respect in the different species ; but the 

 males are constantly distinguished by an oblong patch of 

 erectile clawlike spines on each pectoral fin, and by having 

 the teeth (all, or only a portion) pointed, and not obtuse, like 

 those of the females. In Sharks no secondary sexual differ- 

 ences have been observed; the male Chimccrid<v (see Tig. 

 96, p. 184), possess a singular comblike cartilaginous ap- 

 pendage on the top of the head, which can be erected or 

 depressed into a groove, both the appendage and the anterior 

 part of the groove being armed with booklets. The use of 

 this singular organ is not known. 



The majority of Teleostei are mixogamous — that is, the 

 males and females congregate on the spawning-beds, and 

 the number of the former being in excess, several males 

 attend to the same female, frequently changing from one 

 female to another. The same habit has been observed in 



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