30 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
g. Discussion of Pfeffer’s Work. 
I have purposely omitted, up to this point, any comparisons with 
Pfeffer’s work. He is the only author I have found who deals with the 
twisting in the larval Pleuronectidee from other than the external point 
of view. Unfortunately, he does not give the name of the species on 
which his statements are based, nor are his papers illustrated. 
In his earlier article (’86, p. 4) he describes the general conditions to 
be found in very young Pleuronectidae. The general topography -is 
that of other young fish. The eye sockets —separated below by the 
sphenoid [trabecule cranii ?], above by the ‘‘ Zwischenaugen-Decke ”’ — 
communicate freely with each other in the intervening region. In the 
interorbital and ethmoid regions there is a vertical ridge-like dermal 
bone, having in cross-section the form of an elongated triangle, and sup- 
porting the dorsal fin, which, in Pfeffer’s specimens, reaches to the eth- 
moid. This bone is still free from the cranium, and is the frontale 
principale of authors. 
The bulbus olfactorius, which at first is lodged in the “ Zwischen- 
augen-Decke,” becomes crowded backward into the brain capsule. The 
“Interorbital-Decke ” [supraorbital bart] is bent out toward the eye 
side and twisted somewhat on its long axis, so that its transverse axis, 
previously horizontal, now becomes oblique, slanting downward and out- 
ward toward the ocular side, while the chief part, which was vertical, is 
mostly resorbed by the migrating eye. As a consequence there now re- 
mains between the migrating eye and the surface of the head on the 
ocular side only the thin, glass-like, scarcely perceptible outer skin 
which previously covered the dermal bones. At the same time the der- 
mal bone known as the frontale principale has grown fast to the inter- 
orbital roof-piece, and its course, at first straight from the median crest 
of the brain capsule to the ethmoid, now makes a great bend. Only its 
basal part, in the form of a broad band remains, while the vertical (and 
at first the larger) part has been resorbed. The upper part of the wing 
of the ethmoid on the ocular side has fused with the fronto-orbital, and 
the upper part of its outer margin is continuous with the now develop- 
ing supraorbital cartilage or bone, while the wing of the eyeless side 
remains free on all sides, not forming any connection with the supra- 
orbital of its own side. 
This description of the relations of the wings of the ethmoid to the 
supraorbitals resembles the condition which I have found in Stage 
III a of P. americanus (Figure B, pp. 19, 20) ; but in P. americanus and 
