No. 1— CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 
OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 
COLLEGE, UNDER THE DIRECTION OF E. L. MARK, No. 130. 
Changes accompanying the Migration of the Hye and Observations 
on the Tractus opticus and Tectwm opticum in Pseudopleuro- 
nectes americanus. By STEPHEN R. WILLIAMS. 
TABLE OF CONTENTS. 
PAGE PAGE 
Ey pntroductron) 6020 ks f. Comparison of Bothus with 
Pie WER GERESI GS is. alter ico hve, au) Merry lowe Pseudopleuronectes ameri- 
TT;: Methods ....'. 6 ATUUBT GSN) Mattes! is airy a) eS meas 
IV. Migration of te eye and g. Discussion of Pfeffer’s 
changes in the cartilagi- WOLksl ic) SPIN TKERA TS UTA a 
mous Slowly) 10.1" ben 6 Ty WResume: yf ..¢ ed 
1. Summary of previous ceuilien V. The optic portion of there cen- 
on the migration of theeye 6 tral nervous system . . - 33 
‘2. Description of stages . . . 9 1. General conditioninthe adult 33 
3. Homologies of the anterior 2. The optic nerves . . : seb 
bones of the skull ... Il 3. The chiasma and tracts with 
4. Changes in the cartilaginous related pangliay.. \.))2.6) 4 038i 
SU EU Aat say sah slot ch lidat (Sha vas teas RO 4. The tectum opticum iestey | 
a. Stage I. - . » . . 16| VI. Theoretical considerations . 47 
Beh ce” ORD Set Nes ed at CHO RMS (OS UUNGEEEREI Fie hover Tal yey ee 
Cee Ua ta oh oe Oh IDMOpPAD yA: ONO elite oh SA Naw a eel 
d oe) DEG a tee ee ey ao explanation ot Plates!) 075) (lay) 06 
e Set ME aN iS Vee ns oy edit DB 
I. Introduction. 
THE strange want of symmetry in the head region of flounders 
has attracted much attention especially because in adults both eyes 
occupy the same side of the head. The peculiarity is the more re- 
markable because, for some time after hatching, the eyes and all other 
parts of the head are as symmetrical as in any other fish, and conse- 
quently this asymmetrical condition is brought about afresh in the 
individuals of each generation, instead of once for all, as is the case 
with most variations. 
Regarding the migration of the eye, with a single exception (Pfeffer, 
’86, 94), only such phenomena have been recorded as can be observed 
from surface study or dissections. It has seemed desirable therefore to 
VOL. XL.— No. 1 ] 
