322 



LOWER VERTEBRATES. 



contemporary types aB in the Batrachia Anui-a, but it is none the less universal. The 

 kind of parallelism usually observed is that in which there is only a partial resem- 

 blance between adults of certain animals and the 

 young of others. 



The metamorphoses of these animals have been 

 already referred to, and further details on the sub- 

 ject will be found under the heads of the respective 

 species. I will only note here that while the ma- 

 jority of the Anura undergo a complete metamor- 

 phosis, a few pass through the branchial stage while 

 still in the egg {Sijlodes martmicensis), and other 

 forms carry the young in various ways until this 

 period is passed ; {genera Pipa, Nbtotrema, Opis- 

 thodelphys). 



Fig. 191. — Nototrema marsupiatum with 

 the hrood pouch cut open to show the 



Stjb-Okdee I. — Aglossa. 



There are two families of this sub-order, one of 

 which has no teeth — the Pipidas, and the other has teeth in the upper jaw — the 

 Xenopodidse. In both of them the vertebrte are opisthoccelous ; that is, they are ball- 

 and-socket jointed, with the ball in front and socket behind. The longitudinal epi- 



FiG. 192. — Skeleton of Xenopus ; cor, coracoid ; ecnr, epicoracoid ; 2^^or, precoracoid ; sa, sacrum. 



coracoid cartilages of opj)Oslte sides are distinct, but do not overlap as in Arcifera. 

 The sacral transverse processes are much expanded, and are coossified with the coccyx 

 (Fig. 192). The larvas differ from those of other Anura in having two branchial 

 openings (spiracula), one on each side. 



The family PiPiDiE has the skull completely ossified. It includes but one genus, 

 Pipa, which is only known as existing in South America. The sole species, Pipa 

 americana, is of rather large size, and of exceedingly depressed form. The terminal 

 phalanges are pointed, and the ends of the fingers terminate each in four dermal 



