CHORDATA. SUMMARY OF IMPORTANT FACTS .'.77 



each other, the young (larva-) breathing by gills, the adult by lungs 

 (metamorphosis!). The heart consists of two auricles and one ventricle. 



28. The Amphibia are subdivided into Gymnophiona, Urodela, and 

 Anura; to these are added the extinct Stegocephali. 



29. The Gvmnophiona are blind and have lost the limbs. 



30. The Urodeles have many vertebra? and a well-developed tail. 

 They retain the gills permanently (Perennibranchia), or at least a gill slit 

 (Derotrema), or they lose the branchial apparatus completely in develop- 

 ment (Salamandrina) ; the metamorphosis is not pronounced. 



31. The Anura have few vertebrae, no tail nor gills in the adult, and a 

 marked metamorphosis (the larva.*, tadpoles, are furnished at first with 

 external, then with internal, gills, and with swimming tail, but at first 

 lack appendages and lungs). 



32. Cyclostomes, fishes, and Amphibia are grouped as Anamnia 

 because of the lack of amnion and allantois; they are also called Ichthyop- 

 sida, because of their branchiae and aquatic habit. They are poikilo- 

 thermal (cold-blooded). 



33. The reptiles, birds, and mammals are called Amniota on account 

 of the embryonal organs, the amnion and allantois. They never respire 

 by gills (although gill clefts occur in the embryo), and the appendages are 

 based on the pentadactyle type. 



34. Reptiles and birds are united as Sauropsida from the similar 

 scales and single occipital condyle. 



35. The REPTILIA are poikilothermous, have a strongly ossified 

 skeleton, with unpaired occipital condyle and usually an os transversum 

 in the skull ; a strongly cornified skin, two auricles, and usually two incom- 

 pletely separated ventricles in the heart. 



36. Recent reptiles are divided among the Chelonia, Rhynchocephalia, 

 Squamata (including Lacertilia and Ophidia), and Crocodilia. To these 

 are added the extinct groups Theromorpha, Plesiosauria, Ichthyosauria, 

 Dinosauria, and Pterodactylia. 



37. The Chelonia are compact, have a skeletal capsule (carapace + 

 plastron) composed of bone and horny plates, an immovable quadrate 

 and hard palate, no os transversum or teeth, but horny plates in the place 

 of the latter ; the cloacal opening elongate. 



38. The Squamata have horny scales periodically renewed, a trans- 

 verse cloacal opening, with behind it paired penes, and a movable quadrate. 



39. The Lacertilia have the ventral surface scaled, usually movable 

 eyelids, tympanic membrane, four appendages or their rudiments, and all 

 but invariably a sternum. 



40. The Ophidia lack appendages, sternum, and tympanum; the 



37 



