1880] Structure and Development of Skull in the Batrachia. 437 



These tadpoles, which never see the light as such, have wide mouths 

 (not suctorial), and so also have the tadpoles of the other waif of the 

 sub-order " Aglossa," viz., Dactylethra. In that kind, however, the 

 larvae become large, and are a long while undergoing their transfor- 

 mations, which take place in the water, according to rule. 



In the skull of the adults much variation is evidently due to the 

 different size to which the species attains ; some, as the bull-frog, are as 

 large as the common Greek tortoise, others grow scarcely larger than 

 a bluebottle fly. As a rule, these small kinds show two kinds of modi- 

 fication — they are apt to retain certain larval characters, and they are 

 apt to acquire generalized characters, such as do not normally appear 

 in this group, which is very remarkable for the fewness of the parts or 

 elements composing the adult skull. 



Some of the large forms, as Bana pipiens, have many investing 

 bones in their skull, such as must be looked for again in archaic and 

 extinct types, whilst others, as Geratoplirys and Calyptoceplialus, have 

 a cranial armature that is dense, extended, and almost " ganoid ; " 

 this kind of skull, however, is found in middle-sized types also, as in 

 Pelobates and Nototrema. 



In the terminal suctorial mouth of the larva of the Opisthoglossa, 

 the mandibular pier, and its free " ramus M are carried to the front of 

 the head. After transformation, in the larger kinds, the gape is 

 carried behind the head, as in the crocodile ; it can be guessed how 

 much modification such a change as this will necessitate. 



But it is evident that a low suctorial fish, such as the tadpole is, 

 must have altogether a totally different kind of skull and skeleton to 

 that of an active, noisy, intelligent, more or less terrestrial reptile, such 

 as the frog becomes. 



This necessarily great change involves some very curic-as and 

 instructive anachronisms, so to speak, in the appearance of various 

 parts and organs. 



A low suctorial fish would have no fenestra ovalis nor stapes, and in 

 the tadpole it is some time before these appear. 



The low (urodelous) Amphibia have, in most cases, the upper 

 hyoid element suppressed, sometimes it is present, serving as a rudi- 

 mentary " columella awis." 



In most Batrachia this part does not appear until after transforma- 

 tion, and in some kinds not at all. This part especially shows how 

 the individual is gradually changed, and makes it clear why so many 

 variations should occur in genera and even species. 



I have arranged the forms, whose skulls are worked out zoolo- 

 gically, taking in the results of my earlier observations, already pub- 

 lished in the " Philosophical Transactions." 



These now amount to seventy -Jive ; four of these have already been 

 treated of> and of the new types four kinds are only larval ; neverthe- 

 yol. xxx. 2 I 



