8 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
a little farther back than the right. In this specimen the dorsal fin 
reached as far forward as the middle of the left eye. 
Schidédte 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 
rightly, 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 teedifer, 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 
tncautiously 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 aslight 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 higher 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 
