279 



say, as I have only just had my attention attracted to the subject, 

 and I find that a somewhat complete investigation will be necessary 

 to definitely settle the question. 



In Selachians the anterior margin of the nasal velum of Gegen- 

 baur's (No. 15) descriptions would seem to represent the breathing 

 valve of Teleosts, but, if it does, the two wholly separate develop- 

 mental processes that give origin to the nasal chamber and the breath- 

 ing valve of Teleosts must be combined to produce the nasal velum 

 of Selachians. The furrow in Selachians that, by deepening, separates 

 the nasal velum from the underlying parts must be represented by 

 that slight furrow, or groove, that is said by Seydel to connect the 

 olfactory pits of Ceratodus in young stages, but to disappear in older 

 ones. 



Turning now to the Amphibia it is well known that the larvae of 

 Dactylethra have a maxillary tentacle that is strikingly similar to that 

 of Siluroids. In the adult Dactylethra this tentacle is lost, but the 

 block of cartilage that formed, or supported, its base persists, and a 

 small "seed-like ossicle", the septo-m axillary of Parker's descriptions 

 (No. 28), is said by that author to be formed upon its outer surface. 

 This little bone thus seems to have the same relations to the support- 

 ing cartilage of the base of the tentacle of Dactylethra that the maxil- 

 lary bone of Silurus has to the supporting block of its maxillary 

 tentacle, and if the tentacles in the two animals are homologous the 

 bones should certainly be, provided they are of similar origin. From 

 Parker's descriptions of the septomaxillary, not only in Dactylethra, 

 but also in the frog and in Spelerpes, I should certainly have taken 

 it to be of dermal origin, as the piscine maxillary is, were it not that 

 both Bridge and Sagemehl in their references to it, when discussing 

 the so-called septomaxillary of Amia, consider it as a primary one. 

 Fischer (No. 13), however, in the Gymnophionae, and Seydel (No. 41), 

 in certain reptiles, both show a septomaxillary bone that has every 

 appearance of being a purely dermal one; and its relations to the 

 maxillary and vomer bones of those animals are not unlike those of 

 the anterior end of the maxillary bone of Amia to the dermopalatine 

 and vomer bones of that fish. If then the septomaxillary of amphi- 

 bians and reptiles is the homologue of the maxillary of Siluroids, and 

 if this latter bone has been correctly identified, it is evident that the 

 maxillary of, at least, certain of the higher vertebrates can not be the 

 homologue of the so-called maxillary of fishes. This is self-evident if 

 the premises are correct. 



As some slight further evidence in favor of this supposition it 



