582 
SIR. W. K. PARKER ON THE STEIJCTUEE AND DEVELOPMENT 
Summary. 
As the present paper is but a fraction of the work already done on this particular 
plot of ground, I must refer, in making general remarks upon the skull in this group, 
to illustrations only available to the writer, and not to the reader. 
I also want to show the likeness and the unlikeness of the Urodelous type of skull to 
that of the Batrachia ; but the work given before, on the latter, will be profitable for 
that purpose ; I refer to my two papers on the Skull of the Batrachia (Phil. Trans. 
1871 & 1876). 
But these two examples of cranial structure — the Urodelous and the Batrachian — are 
well fitted for comparison with any skulls that are ; for the place of the Amphibia in 
Nature is in the midst of the Vertebrate tribes ; they stand, as it were, at the parting 
of the way, and you can, in leaving them, go back, at once, to the Fishes, or forwards, 
immediately, to the Reptilian, Avian, or Mammalian groups. 
For in these low creatures the morphological force, like a spirit of change, is rife ; 
and although you begin, in their beginning, with the lowest kind of Fish you can 
conceive of, yet you end, in their ending, with a creature whose endowments, by meta- 
morphosis, enable it to tread upon the heel of the very noblest forms. 
If any of the Vertebrata may be said to be generalized , these may, their relations 
are so radiating and complex ; yet they become specialized in structure in many ways, 
anticipating a great deal of what occurs in groups far above them. 
If we compare the Amphibia with any culminating group of a Class, such as the 
Teleostei among the Fish, the Lacertilia among the Reptiles, or the Carinatae among the 
Birds, we shall be struck with the marvellous uniformity of structure in these, and 
the constant variation of the Amphibia — as though the morphological leaven were, in 
them, still in full ferment. 
To come to particulars : Hana pipiens , the Bullfrog, differs in its skull far more from 
that of Bana temporaria, the common kind, than can be seen in the whole Teleostean 
group, if we except the Siluroids and the Mursenoids. 
There is no such difference in the skull of any Carinate bird as is seen between the 
skulls of Bujo vulgaris and Bufo agua. 
To say nothing of the want of uniformity among the low, quasi-larval Perenni- 
branchiate Urodeles, there is more difference between the skulls of the various genera 
of the Caducibranchs than can be seen in those of the families of the Lacertilia. 
The difference between the Urodelous and Batrachian types of skull is of great 
importance, but difficult to express because of the great variability — a variability in 
fundamentals and essentials, and not in slight things. 
First Stage. — In embryos still coiled up in the jelly there are several differences to 
be noted. 
In the Axolotl there is no appearance of the transverse band which runs across the 
frontal wall in the Frog*. 
* In the following comparisons the reader is referred to my papers on the Batrachian skull (Parts I. & II.) 
and to the illustrations in the present paper. The stages spoken of now are the same as I have described in 
these three papers, and I wish not to confuse the text in this part by incessant reference to plates and figures. 
