66 ILLINOIS BIOLOGICAL MONOGRAPHS [66 



Most students have regarded the gastralia of Sphenodon and the Croc- 

 odilia as derivatives from the plates and bars of the Stegocephals. These 

 latter are also suggested as forming the elements from which the clavicles 

 and episterna of the higher vertebrates are derived. In Sphenodon, ac- 

 cording to Osawa (1896) and Howes and Swinnerton (1901), the gastralia 

 develop without any cartilage basis, and, with the single exception of 

 Schneider, no one has ascribed any cartilage stage for the gastralia of the 

 alligators and crocodiles; while Voeltzkow and Doderlein (1901) shows 

 that in Crocodiles there is no cartilage stage in these structures. In short, 

 the great bulk of the evidence goes to show that these so-called abdominal 

 ribs are dermal elements without any cartilage stage. 



Wilder explicitly states that the cartilages he describes in the ventral 

 surface of Necturus lie in the myocommata; that is, entirely deeper than 

 the skin. He compares them to sternal elements. Hence it would appear 

 that other evidence than these intermuscular cartilages must be brought 

 forward to support his thesis. 



According to Moodie, Micrerpeton has well developed nasals, pre- 

 f rentals and elongate maxillaries, all of which are lacking in Necturus. 

 Now if Necturus is to represent the ancestors of the modern Urodeles in 

 which these same elements are present, we have the difficulty of explaining 

 how these bones disappeared from the line of descent and then were re- 

 formed in the later generations. 



Cope regarded Necturus as primitive because it possessed what he 

 called an intercalary bone in the skull, an element which he also recognized 

 in the Stegocephals. But Kingsbury (1905) says, that, at least in Necturus, 

 Cope's intercalary was the caudal extension of the opisthotic. 



Nothing is known of the cartilaginous nasal capsules of the Stego- 

 cephala, so that no comparison can be made between those of Necturus, 

 and Micrerpeton. However, the complete isolation of the Necturan cap- 

 sule and its wide separation from that of the other Urodeles, is certainly 

 one argument against the ancestral position of this animal. Furthermore, 

 the absence of maxillaries, nasals, and prefrontals in Necturus is one of the 

 arguments of Kingsbury (1905) in regarding Necturus as a permanent 

 larva, a conclusion which a study of the nasal capsule suggests. 



Moodie (1916, p. 24) says: "The condition found in the skull of Crypto- 

 branchus alleghaniensis will represent pretty accurately the condition of 

 most of the coal measures Amphibia." Farther than this no emphasis is 

 laid upon the primitive condition of Cryptobranchus. However, because 

 of the simplicity of the nasal capsule, the persistence of the pterygo- 

 quadrate arch, and also because of the time' and manner of the ossification 

 of the skull, I am inclined to regard Cryptobranchus as more primitive. 



As a study of the nasal capsules suggests, the 'Urodeles are widely 

 separated from the Anura. Fossil Anura occur in an excellent state of 



