210 PROF. W. K. PAEKER ON TIFE STRUCTURE AND 



the suspensorium ; whilst one type, viz. Banodon siliricus (op. cit. pi. v. figs. 68-70), 

 finishes its suborbital band by confluence of the pterygoid cartilage with the ethmo- 

 palatine, a secondary condition answering to that which {summary in the "Anura." 



But the specialization of the Newt, as a typical metamorphosed Urodele, is quite 

 as noticeable for what is left out as for what is developed : the presence of certain 

 elements in other types is, in them, indicative of a somewhat generalized constitution. 



The finished skull of the Newt is similar to and yet very diff'erent from that of the 

 Common Frog ; it is much more ossified, although smaller, has no cavum tympani, 

 no columella, an open jugal space, but with the quadrate region well ossified intrin- 

 sically. 



It keeps the main roof-bones distinct, has no postorbital process to the squamosal, 

 whilst, after giving off a pterygoid bone, the palatine coalesces with the vomer, and, 

 instead of applying itself to the ethmopalatine cartilage — its own endoskeletal counter- 

 part — whilst that is transversely placed, the bone runs backwards at a right angle to it, 

 reaching nearly to the auditory region. 



Hence we see that under the outward likeness of these two small Amphibian skulls 

 there lie hidden a number of the most remarkable contrasts ; these contrasts, however, 

 are not greater than those which exist in the primordial chondrocranium of the larvae 

 of these types. 



Passing from the " Elasmobranchs," in which the placoid dermostoses are not brought 

 under the influence of the slightly calcified chondroskeleton, to the " Ganoids," in 

 which the larger and more perfect dermal scutes are subjected, in the head and 

 shoulders, to the organic attraction of the parts beneath, we perceive a gi-eat difi'erence. 



The scutes of the fore part of the animal are manifestly the " serial homologues " of 

 those of the hind part ; but in size, number, and form they are greatly changed ; some 

 have been selected for one purpose, and some for another. 



The principal regions of the brain, the sense-capsules, the apparatus of the mouth, the 

 hyobranchial arches — all these draw unto themselves such scutes as they need for pro- 

 tection, and for the finishing of the mechanism of the mobile arches. 



Still many of the scutes are simply a repetition of those on the body, and only a 

 certain number stand out as distinguished from the rest by their size, their form, and 

 their relation to the deeper structures. 



These are seized upon by the morphologist as representatives of the superficial 

 bones that, in higher types, have been selected for various functions, that have been 

 completely transformed in accordance with their new relations, and that in those 

 higher forms lose their surface-layers and exist only as subcutaneous bony plates that 

 often combine with the deeper skeletal structures to form the highly compounded 

 skuU. 



If we make a stride, at once, from such a skull as that of Lepidostens to such a skull 



