a a | i 
eee ee a eS 
1885.] Zoology. 189 
strate its homology with the pseudobranchia of the sturgeon. As 
there can be no doubt of the homology of the pseudobranchia of 
Amia with that of the Teleosts, it follows that it is the “ opercu- _ 
lar” gill and not the spiracular gill which disappears in the Tele- 
osts. Dohrn has recently defended this from another stand- 
point. Johannes Mueller’ sview is in opposition to that of Gegen- 
baur 
ur. 
The pseudobranchia appears to be represented in Lepidosteus 
by a mere anastomosis. That genus, has, however, an “ opercu- 
lar” gill (absent in Amia), the two parts of which, although differ- 
ing in their vascular supply, correspond to the complete opercu- 
lar gill of the sturgeon. Balfour was unable to find this gill in 
young specimens of an inch in length. I have arrived at the 
above result from the study of specimens of two inches. 
3. On the auditory organ of Hypophtha/mus.—In a recent paper 
I described the connection between the air-bladder and auditory 
organ in the catfish (Amiurus), paying special attention to the 
morphology of the’ modified anterior vertebrz which establish 
this connection. 
Reissner had previously pointed out that in many tropical Silu- 
roids this “ Weberian apparatus ” is much reduced, but his identi- 
fication of the altered vertebre is so out of harmony with my 
results that I was glad to be able to re-investigate the matter 
through the liberality of Professor B. G. Wilder, who put at my 
disposal last spring a number of the forms in question as well as 
others. As was to be expected, the four anterior vertebrz are 
always modified in a similar manner throughout the group. 
„The genus Hypophthalmus, according to Günther, presents an 
exception to the other Siluroids, in that the anterior vertebrz are 
not united, but as a fact this genus exhibits an extreme type of 
reduction of the Weberian apparatus. The four anterior verte- 
bre are not only united, but the first three of them are tele- 
scoped, as it were, into the occipital region of the skull, so that 
a frontal section through the plane of emergence of the third 
pair of nerves, falls also through the saccu/i of the auditory laby- 
rinth. The air-bladder is represented by two entirely separate 
bladders, about 2™™ in length by 3™™ in width, almost entirely 
enclosed in osseous capsules, situated on either side of the fourth 
vertebra, and coalesced with it. These osseous capsules repre- 
sent the crescentic ossifications in the external tunic of the air- 
bladder of the catfish which are attached to the posterior ends of 
the “ mallei” All the Weberian ossicles are represented, but the 
whole apparatus is so reduced as to be obviously quite func- 
tionless. In conformity with this the /agenar parts of the audi- 
tory labyrinths are much smaller than in the catfish, while the 
saccult of opposite sides still communicate by a transverse duct. 
In compensation, as I think, for the reduction of the Weberian 
apparatus, the neuromastic canals of the head and trunk are 
