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PROF. E. S. GOODRICH ON A NEW TYPE OF 



worked out by Swinnerton in Salmo and Gasterosteus (7), by Derjugin in 

 Essoccetus (1), and by Haller and by Vogel in Salmo (4 & 9). These 

 authors have ascertained that the endoskeletal girdle and fin-skeleton arise 

 from paired rudiments widely separated. From each rudiment develops a 

 procartilaginous plate in which become differentiated the fin radials and the 

 girdle. The coracoid process of. the latter grows downwards and forwards, 

 and may even meet its fellow of the opposite side, without, however, fusing 

 with it. A posterior process grows out behind, and subsequently dwindles 

 and disappears in the adult. In Clupea, I find that the girdle arises in just 

 the same way from paired rudiments, and that its subsequent history differs 

 only in the formation of the transverse bar by fusion across the mid-ventral 

 line. 



As to what significance should be attached to the peculiar structure of the 



Fig. 6. 



Clupea sprat-tits, 36 mm. 

 Cartilaginous skeleton of the pectoral fins and girdle. 



cartilaginous girdle in CHupeids described above, it would be rash to come to 

 any definite conclusion before the corresponding stages in the development 

 of allied forms have been studied. Two points may, however, be noticed: — 

 (1) that the condition when the two halves form a continuous bar is 

 transitory, the girdle being of paired origin and the halves separating again 

 in later life when the dermal bones become well-developed ; (2) that in no 

 other Teleostomes, however primitive, do we find the paired elements of the 

 girdle fused in the middle line. Therefore we can hardly suppose that 

 the cross-bar represents an ancestral condition ; rather would we suggest 

 that it may be a specialisation due to the necessity of affording a firm base 

 of support for the large pectoral fins in young Clupeids, which are active 

 swimmers. 



