20 PROCEEDINGS OF THE AMERICAN ACADEMY 



extended to point of a vertical passing through the lower extremity 

 of the upper jaw. The patches of color which are to be even- 

 tually characteristic of the species first make their appearance in 

 this stage. 

 Fig. 2. Somewhat more advanced than fig. 1. The left eye, when seen from 

 the right side, projects slightly in advance of the frontal. The 

 dorsal and anal fin-rays are well developed, but still united to the 

 caudal. The tail has become rounded. The patches of coloring are 

 defined. Kudimentary ventral fins have appeared. There are as 

 yet no hard rays in the pectorals. 



„ 3. In this stage, the left eye has moved more towards the crest of the 

 snout, the dorsal and anal fins are disconnected from the caudal, 

 and the ventrals are larger than in the preceding stage. 



„ 4. More than half the left eye is seen above the frontal ridge ; the dorsal 

 and anal still more disconnected from the caudal than in the pre- 

 ceding stage; the ventrals larger, and the pattern of coloration 

 quite marked by prominent pigment cells. 



„ 6. In this stage, the left eye has fully passed to the right side, the dorsal fin, 

 extending to the upper edge of the orbit, having gradually extended 

 in that direction from stages represented in PI. IV. figs. 2, 3, 4. 

 The pattern of coloration of the body and of the fins is like that 

 of the adult, but, of course, more indistinct. The dorsal and anal 

 fins are now completely isolated from the caudal fin : they have 

 both fin-rays fully developed, and have greatly increased in breadth 

 since the last stages figured. 



PLATE V. 



Figs. 1-5. — Pleuronectes Americanus Walb. 



Fig. 1. Head of a young specimen, about in condition of PI. III. fig. 1. Seen 

 from above, to show the symmetrical portion of the eyes. 



„ 2. Head of another specimen, about in the same stage as in fig. 1. Seen 

 from below. 



„ 3. Head of a young specimen somewhat more advanced, in which the 

 left eye has changed its position somewhat, and has advanced 

 towards the snout ; showing the effect, when seen from above, of 

 the first movement of translation of the eye of the left side. 



„ 4. Head of young Flounder, intermediate between figs. 4 and 5, PI. III., 

 to show the transfer of the left eye above the ridge of the frontal 

 bone. 



„ 5. The head of a young Flounder, nearly in the same condition as fig. 4. 

 Seen from the left side, showing the position of the eye during the 

 transfer while projecting above the frontal bone. 



Figs. 6-13. — Pseudorhombus maculatus Stein. 



Fig. 6. Head of young specimen still in the egg. Seen from above. The eyes 

 symmetrically placed at extremity of a transverse axis at right 

 angles to the longitudinal axis of the Flounder. 



