232 JouRNAL OF COMPARATIVE NEUROLOGY. 
commissure. It may, therefore, represent both the post- 
temporal and the extra-scapular fused, though I find no direct 
evidence of such fusion. Fig. 1 of the paper referred to shows 
this bone (marked £. S.) just cephalad of the point of separa- 
tion of the commissural canal from the main canal. The com- 
missural canal extends practically no farther mesially than here 
indicated, but the dorsal limb of the bone continues much 
farther, articulating with the cranium not far from the median 
line over the point of union of the posterior and anterior semi- 
circular canals (Cf. Fig. 5, loc. ‘cit.).. The bone has the 
characteristic Y-shape and the ventral limb (shown in Fig. 1 
referred to above ventrally and mesially of the lateral line 
canal) articulates with the skull far ventrally of the other 
articulation. The caudal limb articulates with the shoulder 
girdle in the usual way and carries the main lateral line canal to 
its tip. The bone as a whole should therefore unquestionably 
be called the post-temporal. 
3. Lhe pit organs. 
Fig. 12 illustrates a section taken through the middle of a 
typical small pit organ stained by WeEIGERT’s method after 
fixation in FLEmmine’s fluid. The structure is essentially 
similar to that of the canal organs, with large pear cells among 
the indifferent supporting cells. I have not noticed in my prepar- 
ations a cupula, or debris of cilia over these organs, but quite 
probably the cilia occur, as the prolonged treatment in 
FLEMMING’s fluid which my specimens received is not favorable 
for the preservation of such structures. The aperture by which 
the pit communicates with the surface is a very minute pore, 
round or nearly so, not a slit as in the case of some ganoid 
fishes and of the pit organs of Ameiurus catus as described by 
WRIGHT (’84, p. 267). The latter author gives a description 
in the passage cited of pit organs in young Ameiurus catus 
which corresponds very closely to what I find here. In the 
specimen which I figure here the pit seems to have shrunken 
inward somewhat under the influence of the reagents. Normally 
the pore opens out on unmodified body surface, which is 
