SECRETORY SACS IN TELEOSTEI. 553 



that in tlie Amniota, except that the upward rotation of the 

 external nostril does not take place. In the Teleostei, lastly, it 

 was believed that the homology still holds good, and that both 

 nares are rotated outward aud upward. Hence the posterior 

 nostrils of the Teleostei would be homologous to the external 

 nostrils of the higher Vertebrates, and the anterior to their 

 internal nares. 



These generalizations have been in part confirmed and in part 

 refuted by more recent workers. Por the Teleostei, Sagemehl *, 

 though believing that he was refuting Balfour's view, in reality 

 corroborated it. For the Dipnoi, Semon t has shown that the 

 nares develop as Balfour suggested ; and he thus confirms 

 Huxley's couclusious (Z. c), drawn from a comparison of the 

 adult conditions, that, as concerning their nostrils, the Dipnoi 

 and cartilaginous fishes are closely related. An important 

 modification of Balfour's view has, however, to be noted. In the 

 Dipnoi the communication between the nose and mouth is naso- 

 labial, not naso-pharyngeal, the posterior aperture being morpho- 

 logically disposed external to the teeth which arise on the vomer 

 aud palatine bones. Further, there is no true "palate"; and 

 the question whether the maxillas of fishes are truly homologous 

 with the maxillae of the higher Vertebrates is left open (Semon, 

 I. c, p. 45). As regards the internal nares, it is thus evident that 

 no true homologue to that of Cynoglossiis exists in the class 

 Pisces. 



In the higher Vertebrates, however, if the internal nares arise 

 secondarily in the Amphibia, as suggested by Balfour, there is 

 the possibility of such an homology. Hochstetter J, however, has 

 thrown doubt upon the whole of Balfour's conclusions with 

 regard to the origin of the internal nares in the Amniota. He 

 shows that the "palate" is not formed by the maxillary bones, 

 but by the fusion of the external aud median primitive nasal 

 processes, and that the internal nares then arise secondarily by 

 the perforation of the palate. These observations were made 

 upon certain mammalian forms ; aud in the same forms as well as 



* Sagemebl, M. : "Das Cranium toii Amia calva, L." Morph. Jahrbuch, 

 Bd. ix. p. 221. 



t Semon, E. : " Die aussere Entwickelung das Cerailoi'MS i'brsifm." Denksch. 

 der Med.-Naturwiss. Gesellsch., Jena, Bd. iv. 1893, pp. 44-45. 



+ Hochstetter, F. : " Ueber die Bildung der inneren Nasengange oder 

 primitiven Choanen." Verb. d. Anat. Gesellsch. 1891 (Anat. Anz. Bd. vi 

 Suppl.) p. 145. 



