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 Déderlein (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 derma] 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- 
frontals 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 
