OP ARTS AND SCIENCES. 295 



form, but they are far less advanced than those of the caudal. The 

 embryonic fin rays are still to be traced in that part of the fin fold 

 which unites the caudal lobe with the dorsal and anal. The coloring 

 of this stage is greener than in the preceding stages ; the greenish 

 tint is especially marked on the upper part of the head and near the 

 I dorsal patch of chromatophores. The ventrals are somewhat darker 

 colored than the younger stages. In all the stages thus far figured the 

 young fish swims mainly by means of the powerful stroke of the 

 ventrals, which they spread like wings laterally to their fullest extent 

 at right angles to the body. In a somewhat more advanced stage 

 (Plate VII. fig. 5), measuring 12°^^ in length, the body has increased 

 greatly in length, the pectorals are longer, the ventrals are less than 

 one-fourth the length of the body ; the caudal has become terminal 

 and rounded, and quite well separated from the dorsal and anal ; the 

 permanent fin rays are well developed in the three median fins ; the 

 head has become lengthened, and the pigment spots of the upper part 

 of the head and anterior part of the body are smaller and more 

 numerous than in the preceding stages. 



The chromatophores along the dorsal line and base of the dorsal 

 and anal are now arranged in longitudinal lines. The coloring of the 

 body behind the anterior base of the dorsal, as well as the head, has 

 assumed a yellowish-green tint slightly bluish towards the ventral 

 side. 



In a subsequent stage (Plate VII. fig. 6), but slightly older, the 

 greenish color of the dorsal part of the fish has become more marked, 

 and there exists a principal lateral line of black chromatophores 

 extending from the operculum nearly to the posterior extremity of the 

 dorsal ; the extremity of the body near the caudal is still quite trans- 

 parent, of a yellowish tint, showing the ganoid termination of the 

 notochord. The ventrals in this stage are proportionally longer 

 again than in Plate VII. fig. 5, being somewhat more than one 

 quarter the length of the fish. Viewed from above, the young 

 fish is often seen with ventrals spread at right angles, as in Plate 

 VIII. fig. 1 a, or flapping them violently up and down when excited, 

 or as in Plate VIII. fig. 1, when swimming rapidly. In a somewhat 

 older stage (Plate VIII. fig. 2) the dorsal and anal fins are well 

 separated from the caudal ; the anterior dorsal has commenced to 

 form ; the ventrals have lost somewhat their wing-like character, 

 they are usually carried folded^ and appear more like long fin rays ; 

 the head has lengthened, is more rounded, sloping anteriorly ; the 



