8 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



a little farther back than the riglit. In this specimen the dorsal fin 

 reached as far forward as the middle of the left eye. 



Schiodte held from these observations that the dorsal fin kept its po- 

 sition and that the left eye migrated forward around it and then passed 

 backward to its final position. His implied argument, if I understand him 

 riglitly, is, that the right eye moves backward from a position over the 

 lower (posterior) third of the maxillary bone to one over its lower (pos- 

 terior) extremity, and that the left eye moves backward still further 

 proportionally, because in the end (the 40 mm. specimen) it is not only 

 above but "a little behind " the right eye. This conclusion was in his 

 opinion confirmed by the observation that the rays in the dorsal fin of 

 young specimens corresponded in number with those of the adult. 



He described under the name Bascanius taadifer, n. s., a peculiar 

 flounder (evidently sinistral), which had a semilunar depression between 

 the right eye and dorsal fin. Here the body was so thin that, if 

 incautiously handled, it broke in pieces or separated itself from the 

 dorsal fin. In that case a part of the right eye appeared through the 

 hole, giving the animal the appearance of possessing two eyes and a 

 half. 



Agassiz ('78) described definitely for the first time the two methods 

 of development by which the eyes of flatfishes change position. His 

 description of the method by migration around the head is briefly as 

 follows (p. 5) : " The first change — and the process is identical, 

 whether we take a dextral or sinistral flounder — is the slight advance 

 toward the snout of the eye about to be transferred. . . . This move- 

 ment of translation is soon followed by a slight movement of rotation ; so 

 that, when the young fish is seen in profile, the eyes of the two sides no 

 longer appear in the same plane, — that on the blind side being slightly 

 above and in advance of that on the [future] colored side. With increas- 

 ing age, the eye on the blind side rises higiier and higher toward the 

 median longitudinal line of the head ; a larger and larger part of this 

 eye becoming visible from the colored side where the embryo is seen in 

 profile, until the eye of the blind side has, for all practical purposes, 

 passed over to the colored side." 



Later the dorsal fin finds its way forward toward the nose, dorsal to 

 the transposed eye. 



Agassiz also well described the method by penetration discovered by 

 Steenstrup in Plagusia. The change was followed day by day in fishes 

 kept captive in his Newport laboratory. He pointed out that these two 

 methods are merely two extremes of the same process ; probably the 



