LIPS AND NASAL APERTURES IN FISHES 191 
Dohrn (’04, fig. 9, pl. 16), in a median sagittal section of an 
embryo of Torpedo, shows what would seem to be the primary 
upper lip lying posterior to the hypophysis, and it is shown as 
formed of ectoderm on its external, and of entoderm on its 
internal surface, as if it were a remnant of the oral plate. His 
however shows (92 b, fig. 26), in a median sagittal section of an 
embryo of Pristiurus, a dermal fold immediately anterior (aboral) 
to the hypophysis which he calls the upper lip of the fish, and in 
a similar figure (His, 792 a, fig. 14) of an embryo of Scyllium, 
what is apparently this same fold, but not named, is shown in a 
similar position. There is, however, in both these figures of 
His’s, a larger but lower fold of the ectoderm, oral to the hypoph- 
ysis, in the place occupied by the fold in Dohrn’s figure of Tor- 
pedo. It may then be that the fold called by His the upper lip in 
his figure of Pristiurus is a secondary and not a primary lip. 
Comparison with Lundborg’s (’94) figures of Salmo salar would 
seem to show that'this is the case. In this latter fish Lundborg 
shows, in median sagittal sections, a large rounded eminence, 
rather than a fold, immediately anterior (aboral) to the hypo- 
physial invagination, and anterior to it there is a small ecto- | 
dermal fold projecting postero-ventrally from the posterior 
surface of the rounded anterior end of the snout. The low and 
rounded eminence is said to later become a part of the dorsal 
surface of the buccal cavity, and it seems quite unquestionable 
that the small ectodermal fold immediately anterior to this 
eminence becomes the maxillary breathing-valve. The func- 
tional upper lip of the fish, which is here unquestionably a 
secondary one, must then lie anterior to this breathing-valve, 
and hence must be developed from tissues on the ventral edge of 
the rounded anterior end of the snout, and it would seem to be 
shown, in process of development, in His’s (’92 b, fig. 31) figure 
of a sagittal section of a 20 mm. trout. If then the small fold 
which I take to be the maxillary breathing-valve be that valve 
and not the primary upper lip, the latter lip must either be repre- 
sented in the low and rounded eminence which becomes part of 
the dorsal surface of the buccal cavity, or it must lie posterior to 
the hypophysis; and as, in the younger embryos figured by 
