174 EDWARD PHELPS ALLIS, JR. 
internal surface of the naso-labial fold of that fish. The fold of 
the secondary upper lip of Chimaera would then have been inter- 
rupted, as it is in the Plagiostomi, by its encounter with the 
original postero-mesial nasal aperture and not by its encounter 
with the antero-lateral aperture, as it would have been if that 
aperture of the Plagiostomi were, as Hubrecht considered it to 
be, the homologue of the postero-lateral aperture of Chimaera. 
The folding back of the nasal flap would give rise, as already 
stated, to the rounded fold at the lateral end of the thick pre- 
maxillary upper lip of Chimaera, and the latero-oral corner of 
the fold might have been perpetuated in the little teat-like 
eminence on the mesial surface of the newly formed antero- 
mesial nasal aperture. 
The ala nasalis would naturally undergo modifications during 
these changes in the nasal apertures, that part of it which en- 
circled the original antero-lateral aperture undergoing reduction, 
and the part which encircles the newly formed antero-mesial 
aperture undergoing special development. This latter aperture 
would be external and aboral to the position occupied by the 
original postero-mesial aperture, and that part of the ala nasalis 
which encircles it (cartilage ‘kn’) would have the appearance of - 
having been pulled or stretched upward and outward from the 
nasal capsule, as it actually has in Chimaera. <A remnant of the 
process 6 would remain in the ridge on the internal surface of 
the naso-labial fold, and such a remnant is actually there found. 
The process a’ would become the longitudinal valvular surface, 
found, in Chimaera, on the internal surface of the large valvular 
process (process a), and it would acquire a new valve-seat near 
the lateral edge of the newly formed premaxillary lip. The 
cartilage ‘l’ of Hubrecht’s descriptions, above referred to, and ~ 
possibly also the little eminence on the dorsal surface of the 
ala nasalis (cartilage ‘kn’), would represent persisting remnants of 
that part of the ala nasalis which originally encircled the antero- 
lateral nasal aperture. 
During these changes in position of the nasal apertures, the 
antero-lateral and incurrent-aperture would remain connected 
with the exterior through the passage between the external sur- 
