SKIN, SCALES, AND SPINES 



95 



the development of the plates. As far as the British Isles are 

 concerned, indi\'iduals from inland waters nearly always 

 exhibit the reduced number of plates, whereas examples from 



Fig. 42. ARMOURED FISHES. 



A. Hassar or Cascadura {Callichthys littoralis), X ^ ; b. Pogge or Armoured 



Bullhead (Agonus cataphr actus), Y.l\ c. Mailed Cat-fish (Plecostomus garmani), 



xi; D. Trigger-fish {Balistes capnscus),xi ; e. Pine-cone Fish {Monocentris 



japonicus), X^ ; F. Trunk-fish (Lactophrys trigoniis), X ^ ; g. Porcupine-fish 



{Diodon hystrix), X i ; H. Shrimp-fish or Needle-fish {Aeoliscus strigatus), X ^. 



the sea are fully armed, intermediate types occurring in 

 estuarine waters. Individuals from still more southerly localities 

 may lack plates altogether. 



It has been seen that the past history of fishes reveals a story 

 of gradual improvement in heavy armour, followed by a definite 



