Pps BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the chiasma, but he further remarked that this relation is not constant, 
and that individual differences occur. Owen (66, p. 300) observed that 
the nerves cross each other without interchange of fibres, and that some- 
times the nerve of the right eye is dorsal, as in the hake, and sometimes 
that of the left, as in the halibut. He added in a note that both con- 
ditions had been seen in different individuals of the cod. Gegenbaur 
(98, p. 796), in his recent comparative anatomy, reiterates the chief 
statement made by Stannius; namely, that the right nerve is usually 
dorsal, but he cites no examples supporting this opinion. C, J. Herrick 
(99, p. 394), in his work on Menidia, remarks that in this fish the 
left nerve is dorsal, as “is typical for teleostomes,” and in this state- 
ment I understand him to mean the nerve connected with the left eye, 
an interpretation already put on this passage by Cole and Johnstone 
(:01, p. 116). Finally Greeff (:00, p. 25), in the new edition of the 
Graefe-Saemisch Handbuch der Augenheilkunde, reaffirms the statement 
originally made by Stannius that the right nerve is dorsal. Thus there 
is a difference of opinion as to which nerve usually is dorsal,—a con- 
dition of affairs that can be cleared up only by reinvestigation. 
Much of the material upon which the following studies were made, 
was either from the collections of the Museum of Comparative Zodlogy 
or from those of the United States Fish Commission. To the officers of 
both these institutions I express my grateful thanks. The materials 
obtained from each of the two sources are indicated by foot-notes in con- 
nection with the Tables; material not otherwise designated was obtained 
by myself. 
II. Positions of the Nerves in the Chiasmata of Symmetrical 
Teleosts. 
To ascertain whether the right nerves or the left nerves are more 
usually dorsal at the chiasmata of symmetrical teleosts, I examined a 
hundred specimens each of ten common species. The results of this 
examination are given in Table I., in which the columns opposite the 
name of the fish show the number of instances of right nerves dorsal 
and of left nerves dorsal in a total of one hundred cases. These two 
conditions, as Owen (’66, p. 300) long ago observed, are well shown in 
the cod (Figs. 1 and 2). 
This table shows that in six of the ten fishes examined (Fundulus, 
Rhombus, Stenotomus, Tautoga, Prionotus, and Melanogrammus) the 
left nerve was dorsal about as frequently as the right, the greatest dif- 
