586 
ME. W. K. PAEKEE ON THE STETJCTURE AND DEVELOPMENT 
Teleostei, but are deficient in segments ; in the Batrachian they are manifestly merely 
a modification of the Marsipobranchiate type, and the inner rods are arrested*. 
Fourth and two or three following Stages. — Some minor stages may be considered 
together now, so as to bring the Axolotl up to its Cryptobranchiate stage, and the Frog 
to the time when its second series of gills are losing their functions; we can then 
compare the skull of the adult in each type. 
In the Axolotl the hind part of the cranial notochord acquires a new pair of cartilages 
to invest it — the parachordals. I am not certain of their perfect distinctness in the Batra- 
chian; their nasal roof is not so distinct from the trabeculae in front as in the Urodeles. 
Very soon in both cases there is a continuous basal cartilage from the occipital condyles 
to the frontal wall ; for in both cases the trabeculae become continuous with the basal 
cartilages behind, grow together between the nasal sacs in front, and send out two free 
cornua. 
In the Axolotl neither a roof nor a floor of cartilage is ever formed in the middle or 
interorbital region of the skull ; in the Tadpole a floor soon forms between the divari- 
cated trabeculae. 
In the Axolotl a slight ethmoidal roof is formed in front and an occipital roof behind ; 
but besides these, which are better developed in the young Frog, there is also in it a 
band of cartilage (tegmen) over the posterior sphenoidal region. 
Whilst the Frog continues larval the palato-quadrate band remains as a short, joining 
tract, and the pedicle remains continuous, behind, with the trabecula. 
In the Axolotl after two or three weeks an “ ethmo-palatal ” cartilage grows from the 
trabeculae, behind the nasal sacs, and a process of cartilage grows forwards from the 
front of the suspensorium ; this free cartilage and that process, together, represent the 
jpalato-guadrate band of the Tadpole. 
Of course as long as that band stops in its arrested stage the quadrate hinge runs up 
to the sides of the nasal region, and the mandibles are transversely placed ; this is mar- 
vellously unlike the state of things in an Axolotl larva, large or small. 
The auditory capsules are now well chondrified in both types, and a crescentic slit, 
whose convex edge is outwards, appears beneath the capsule. 
In the Axolotl the thin and ragged edge of the cartilage mesiad of the slit forms itself 
into a leaf of cartilage which becomes free, and shapes itself into the elliptical stapes. 
In the Frog and Toad the soft tissue filling the chink chondrifies separately as the 
stapes. 
In the Axolotl the ascending fork of the pedicle coalesces with the alisphenoidal 
crest of the trabecula, the lower process becomes bulbous, but remains free; the otic 
process is pedate above and embraces the capsule. 
In the Tadpole the pedicle, without any ascending fork, is fixed, and the “ elbow ” 
of the suspensorium is attached to the capsule by a band of cartilage which is pedate 
behind ; this is the 'primary, transitory, otic process — a “spiracular ray,” as in the Sharks. 
* In the Shark there are two sets of arches, outer and inner ; the outer are arrested and the inner developed ; 
the contrary takes place in the Tadpole. 
