-•'iS Mr?. W. K. PARKER ON THE STRUCTURE AND 



the suh-auditory iving of the basal plate, so also does the upper hyoid bar (columelki), 

 and the stylo-hyal end of the lower bar, except, when, as in Phyllomedusa hicolor and 

 Acris Pickeringii, it fuses with the hinder edge of the pedicle. 



D. — What larval structures are retained {in a modified form), and what parts are 



moulted or absorbed. 



Some of the structures are but little changed, but the new things of the permanent 

 creature are rapidly forming ; we can see what is cast off, what is kept, and what 

 things are superadded. 



As to several of the larval structures, the morphological force makes clean work of 

 them ; some are shed, completely, or moulted off, as the horny jaws, dentated rugae, 

 and papillose oral appendages. Wliilst the huge upper labials are absorbed, the lower 

 labials are used for making the "chin" of the adult; the spiracular cartilage — coming 

 in slowly — is kept to form the annulus tympanicus, but the four pairs of " extra- 

 branchials" are absorbed, and remnants only of them and of the true inner visceral 

 arches are retained. A summer Bee-hive is not a more lively place than a Tadpole's 

 organism at this stage ; every cell is busy, every element is moving, working, and 

 changing ; the size, shape, and direction of organs and parts are all being lessened, 

 or made larger ; moulded into new shapes, and turned fore or aft, outwards or in- 

 wards, as the governing force listeth. As the result of all this working towards a 

 new zoological end, that which began life as a Fish but little higher than a Lamprey, 

 fulfills its after-life as a Reptile but little lower than a Turtle. 



After the horny jaws and dentated horny rugte have been moulted, before the upper 

 labials have been absorbed, a new pair appear on each side, attached to the nasal 

 processes of the premaxillaries and to the outer nostrils. The lower labials become 

 relatively less, get into a line continuous with that of the mandible of the same side, 

 coalesce with those bars and become ossified by the grafting of the dentaries upon them. 



The " orbitar processes," after their transportation to a post-oral position, become, 

 in most cases, quite absorbed ; so also, in most cases, does the upper part of the 

 pedicle ; it is retained in some, as in Bufo vulgaris, where the pterygoid bone binds 

 down upon the " lobe," or the sub-apical, enlarged part of the pedicle. 



The "spiracular cartilage" may chondrify continuously, either with the "elbow" of 

 the pedicle (otic process), or with the tegmen tympani. It may become lessened in 

 size, considerably, before it takes on its adult form, as the annulus tympanicus. 



As I have said, the four other outer cartilages belonging to the 3rd, 4th, 5th, and 

 6th arches, viz. : the exti'a-branchials, become almost entirely absorbed ; in some cases 

 the proper hyoid bar does, also. 



I believe that I am right in calling the larval rudiment of the " annvdus tympanicus" 

 the spiracular cartilage; 1 put it into the category of the " inter-branchial rays" — as in 

 the Sharks ; the "tegmen tympani" is the " extra- visceral" tract from which it grows, 

 as a rule. 



