46 ILUNOIS BIOLOGICAL MONOGRAPHS (46 



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 branous partition separating the internasal space from the cavum cranii. 



It would follow then, that Diemictylus is probably reduced from some 



form like Triton, and both genera are related to Salamandra which has 



developed along a line parallel to Amblystoma; and it is through some 



Spelerpes-like larva, as far as the nasal capsules are concerned, that 



Salamandra, Triton and Diemictylus are related to the group including 



Plethodon and Amblystoma. 



Necturus and Proteus have often been regarded as primitive and Cope 

 (1889) included them in a group, Proteida, apart from the Urodeles, 

 although ancestral to them. I have not examined Proteus, but upon the 

 basis of the nasal capsule of Necturus, which cannot be regarded as ances- 

 tral. Cope's position can not be affirmed. Pinkus (1894) called attention 

 to the similarity of the nasal capsules of Necturus and Protopterus, a 

 similarity based wholly upon the fenestration of the capsules, and not upon 

 structural resemblances. The parts of the capsule of Necturus may be 

 homologized with those of other Urodeles, but many differences have arisen 

 in the appearance of these parts, so that relationships are very remote. 

 Many parts of the capsule chondrify independently, later uniting to each 

 other; the ethmoidal column, hovfever, never unites to the other parts of 

 the capsule, but by lateral growths produces the fenestrated roof over the 

 nasal sac. Necturus is greatly retarded in the development of its nasal 

 structures. In a 25 mm. larva only trabeculae are present, there being no 

 evidence of cornua or planum basale or columnae, as in corresponding ages 

 of Amblystoma and Salamandra. The earlier larvae of Spelerpes, Des- 

 mognathus, and Necturus seem to resemble each other very closely in their 

 cylindrical trabeculae, slight cornual expansions and absence of trabecular 

 crests. In the later stages, however, further resemblance is lost, for 

 Spelerpes has gained true Urodelan characters while Necturus still possesses 

 larval relationships; a fact, which, together with the retarded process of 

 chondrification, suggests for Necturus that it may be a persistent larva, as 

 has often been suggested. 



As stated above, Cope placed Proteus with Necturus in the Proteida, 

 regarding them as primitive Amphibia, and related to the Stegocephala by 

 the presence of an intercalary bone. Kingsbury (1905) rejects Cope's 

 thesis, affirming the absence of an os intercalare in Necturus, and suggested 

 that Cope had probably regarded the posterior process of the opisthotic 

 as an intercalary; furthermore he regards the intercalary of the Stegoce- 

 phala as a membrane bone. 



Norris (1911) working on the cranial nerves of Necturus, concludes 

 that it cannot be regarded as primitive. The distribution of the cranial 

 nerves agrees in detail with that of the higher Urodeles, a condition which 

 would not be expected in a primitive form. Kingsbury, like others, has 

 regarded Necturus as a neotenic larva, and would place it near Spelerpes. 



