DKAl.FISHES. 



313 



;it least until it is lOU iiini. Ion,!;- ((jxcludiiig the caudal 

 tin), without any reduction ot the long, anterior rays of 

 the dorsal or the ventral tin (tig. 81, a). Sometimes, 

 however, this reduction ai)pears at an earlier pei'iod, tlie 

 elongated, lower rays of the caudal fin also shrinkintr 



In the course of development, however, a great 

 dissimilarity may prevail: tlie same stage of develop- 

 ment is attained earlier (at a smaller size) by one larva 

 and later by another; and we are still far from com- 

 petent to decide with certainty whether this dissimilarity 



'"''^^/K'-A^^y^^... 





Fio-. 81 li. Young Trachijpterus iris from Messina, brought home in 1891 by Dr. Bovallius. Nat. size. 



Fig. 82. Caudal fin of a Trachypteriis iris 42 ram. long, from Messina. Magnified. 



and vanishing, while the upper division of the caudal i depends on a difference of species. \\'e iaiuw, however, 

 tin, which eventually assumes the appearance of a per- | that, at a more advanced age. great individual varia- 

 fect tin, with the two outermost rays strongest and long- ; tions appear in tlie characters of the l)est-known si^ecies. 

 est, takes up a vertical position on tlie dorsal edge of 

 the end of the tail, in the form of an uin'ight ftm (tig. 82). 



Scandin a via n Fishes. 



Emery has shown that, in the Mediterranean Tracluj- 

 pterus iris, the length of tlie head, during the growth 



40 



