DEVELOPMENT 



335 



the fish has grown to a length of sixty milhmetres, even more 

 niarked changes have occurred. The dorsal fin has become 

 diflferentiated into an anterior portion of great size and a 

 smaller posterior part; the upper jaw has grown out still farther 



-^ ^ e. 



Fig. 121. DEVELOPMENT OF SAIL-FISH AND DEAL-FISH. 



A. Three stages in the development of the Sail-fish (Istiophorus, sp.). (After 

 Gunther.) (I) 9 mm., X 3^ ; (II) 14 mm., X 3^ ; (III) 60 mm., nat. szie. A full- 

 grown specimen is shown in Fig. 6a. b. Three stages in the development of the 

 Deal-fish {Trachypterus arctiais). (After Emery and Smitt.) (I) 16 mm., X i\ \ 

 (II) 100 mm., X { ; (III) 1000 mm., x ^V- 



and now projects considerably beyond the lower, and the teeth 

 have all but disappeared ; the long spines from the back of the 

 head have been reduced to comparatively minute proportions, 

 and the filamentous pelvic fi„ns are much smaller. It will be 

 observed that the eye is progressively smaller at each stage. 

 The young Sword-fish (Xiphias) undergoes a very similar series 



