62 



NATURE 



[May 15, 1879 



palatine and pterygoid cartilages appear, and it then 

 subdivides, the pterygoid getting the larger half but no 

 teeth, and the ethmo-palatine the lesser half and all the 

 teeth. The form of these parts varies much in the dif- 

 ferent genera. 



The apparent uniformity of the Batrachia, as to the 

 skull especially, is quite belied by what is found on dis- 

 section. The disposition of parts in the skull varies 

 greatly. 



A careful study of the morphology of the Batrachia 

 suggests many things as to their genetic origin, and 

 accords very accurately with the known facts of their 

 geographical distribution. On the whole the types are 

 more generalised in the west than in the east, and much 

 more so in the south than in the north. 



There is nothing in which the frogs and toads differ 

 more from the salamanders than the extraordinary de- 

 velopment of the middle ear ; the latter always modify 

 a part of the capsule so as to produce a fenestra ovalis 

 and stapes : but in the former, as a rule, the upper ele- 

 ment of the hyoid arch is modified into the chain of the 

 middle ear, the spiracular cartilage into the ring of the 

 ear-parchment, and the skin covering the first cleft into 

 the parchment of the ear drum. In certain kinds of 

 frogs and toads these parts are as much arrested as in 

 the salamanders and newts ; in all of them that part of 



e.ti'- 



A.Ay 



Fig. 4. — Diagram of chondrocranium of yjung Axolotl. The Roman fibres 

 indicate the nerve foramina, a./, ascending process of suspensonum ; 

 att, auditory capsule ; d.ir, basi-branchial ; ^r, branchial arch ; c.&r, 

 ceralo-branchial ; c.h}i, cerato-hyal ; c tr, cjruna trabeculac; <■, eye; 

 e.ir, epi-branchial ; r.Aji, epi-hyal ; e.fa, ethmo-palatine; »./Sr, epi- 

 pterygoid ; I'v, investing mass ; wri, Meckers cartilage ; u/, olfactory 

 capsule; ep, orbital process; /></, pedicle ; }, quadrate ; */, stapes; tr, 

 trabeculac. 



the hyoid arch which is developed into the middle ear- 

 chain is later in its appearance than that which carries the 

 tongue. 



It is evident that the great polymorphism of these 

 types is due to the influence of their surroundings upon 

 them. 



The larger kinds are a long while undergoing meta- 

 morphosis, and in their adult condition they possess many 

 bones which can only be found again in the long-extinct 

 Amphibians of the Coal Measures. With regard to small 

 and arrested kinds, which, as a rule, belong to the Noto- 

 goea, their arrest in metamorphosis can be paralleled with 

 various stages of development in higher kinds. For ex- 

 ample, in Pseudophryne bibronii, a small Australian bom- 

 binator toad, the auditory apparatus is arrested at the 

 same stage in which we find it in our native kind up to 

 midsummer, that is to say, there is no columella ; in 

 Rhinoderma darwinii, a South American form, the 

 columella is a thick short wedge of cartilage terminating 

 externally in a fibrous thread, precisely like the rudiment 

 we find in our own native kinds in the beginning of July ; 

 and in a small African species of frog, Comphobtttes, the 

 columella is developed to the conditio.-! of that of our 

 native kinds a month or two later, and it is not ossified. 



The relative size of the perfect larva to the adult is 

 extremely variable in the Batrachia. In Bufo chilensis 

 the recently metamorphosed young is no larger than a 



common house-fly, the tadpole being about twice the size, 

 and in Pseudis paradoxa, a South American form, which 

 is scarcely larger than our native frog, the tadpole attains 

 the size of a herring or a red mullet. In the case of Pipa 

 monstrosa from Surinam, the young when ready to leave 

 the dorsal pouches of the mother are scarcely as large as 

 a honey-bee, but as perfect in their metamorphosis as the 

 young of our native frog and toad at the end of a year ; 

 the mother toad is twice as large as a large female native 

 toad. 



It is evident that those forms in which the tadpole is 

 of such a large size, have a tendency to remain in the 

 larval condition, and are thus a little in advance of the 

 axolotl, most of the individuals of which are arrested as 

 permanent larvae, a few only undergoing transformation 

 into true gill-less salamanders (/^wj^/y^/o^za). 



The manner in which the different kinds of Batrachia 

 are modified, both as to their outward form and skeleton, 

 each one to suit its own particular kind of life, is very in- 

 teresting and instructive. The little tree-frogs have in 

 their skull a large membranous fontanelle, covered merely 

 with skin, as in young infants ; their toes are flattened, 

 and thus they are able to climb with ease and safety 

 amongst the foliage, the colours of which they imitate. 

 Other forms, such as Pelobates fuscus, living on the 

 ground, have their small brain encased in dense and 

 almost enamelled armour, and besides this protection, the 

 above-mentioned Pelobates, or garlic toad, has the power 

 of giving forth an offensive odour from the skin. This 

 last kind is almost devoid of a middle ear, and the colu- 

 mella is extremely small ; the little tree-frogs, on the 

 contrary, have very perfect ears. Thus in Pelobates we 

 have a skull approaching that of the Labyrinthodonts, 

 while in the tree-frogs the skull resembles very much that 

 of a shark or skate. 



Some large kinds, such as Ceratophrys dorsata, have, 

 besides the dense bony plates covering the head, similar 

 large scutes over their shoulders. 



The frogs and toads that possess a tongue have their 

 eustachian passages wide apart, as in Mammals, but in 

 the tongueless forms, Pipa and Dactylethra, the two tubes 

 meet at the mid line, as in birds. They have all twc^Mj 

 separate occipital condyles, as in Mammals. '^^j 



Taking the Batrachia through and through, they form 

 a wonderfully perfect chain of types ; they do not, how- 

 ever, lead us directly to any existing groups of high Ver- 

 tebrates, but rather look towards Mammalia than in the 

 direction of reptiles and birds. ^ 



Reptiles 



Snakes.— "Wi^ snakes have probably arisen from ances- 

 tors which possessed limbs, which, however, have become 

 inconvenient to their descendants, and have therefore 

 been supressed. The boas and pythons, as well as the^, 

 Typhlopidce and Tortrices, have, however, rudiments o^Hj 

 posterior extremities. "^^ 



There is a certain embryonic simplicity in the mternal 

 skull, but the outer skull is very perfect and marvellously 

 specialised, as is also the spine. There are no exoskeletal 

 elements whatever behind the head, but in the head there 

 are some small cartilages besides the investing bones, 

 which latter form three-fourths of the skull. 



The bones of the skull are the most adamantine to be 

 found anywhere in the vertebrate kingdom, while the 

 cartilage, where it survives (as in the trabe^ula), is per- J 

 fectly elastic, and untouched by the ossifying process. ^ 

 Where sutures persist they are perfectly distinct to old 

 age ; when ankylosis takes place along any particular line 

 it early obliterates the least trace of the original suture. 



A large part of the base of the skull is more simple and 

 embryonic than anything to be seen in the skull of the 



■ Besides the tw) papers in the Philosophical Transactions (1871 and 

 1876), the lecturer is preparing a large memoir on the structure and develop- 

 ment of the ikuU in a large number of larval and adult forms of Batracnia. 



