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MESSRS. F. M. BALFOUR AND W. H. PARKER OK THE 
rather less advanced than in corresponding stages .in bony Fishes; the brain is also 
comparatively smaller, the otolith ellipsoidal, placed obliquely in the rear above the 
gill-opening. . . . Usually the gill-cover is pressed closely against the sides of the 
body, but in breathing an opening is seen through which water is constantly passing, 
a strong current being made by the rapid movement of the pectorals, against the 
base of which the extremity of the gill-cover is closely pressed. The large yolk-bag 
is opaque, of a bluish-gray colour. The body of the young Lepidosteus is quite colour¬ 
less and transparent. The embryonic fin is narrow, the dorsal part commencing above 
the posterior end of the yolk-bag; the tail is slightly rounded, the anal opening 
nearer the extremity of the tail than the bag. The intestine is narrow, and the 
embryonic fin extending from the vent to the yolk-bag is quite narrow. In a some¬ 
what more advanced stage,—hatched a few hours earlier,—the upper edge of the yolk- 
bag is covered with black pigment cells, and minute black pigment cells appear on the 
surface of the alimentary canal. There are no traces of embryonic fin-rays either in 
this stage or the one preceding; the structure of the embryonic fin is as in bony 
Fishes—previous to the appearance of these embryonic fin-rays—finely granular. 
Seen in profile, the yolk-bag is ovoid; as seen from above, it is flattened, rectangular 
in front, with rounded corners, tapering to a rounded point towards the posterior 
extremity, with re-entering sides.” 
We have figured an embryo of 11 millims. in length, shortly after hatching (Plate 21, 
fig. 12), the most important characters of which are as follows:—The yolk-sac, which has 
now become much reduced, forms an appendage attached to the ventral surface of the 
body, and has a very elongated form as compared with its shape just before hatching. 
The mouth, as also noticed by Agassiz, has a very open form. It is (Plate 21, fig. 13, 
m.) more or less rhomboidal, and is bounded behind by the mandibular arch (mn.) and 
laterally by the superior maxillary processes ( s.mx .). In front of the mouth is placed the 
suctorial disc (s.d.), the central papillae of which are arranged in groups. The oper¬ 
cular fold (h.op.) is very large, covering the arches behind. A well-marked groove is 
present between the mandibular and opercular arches, but so far as we can make out 
it is not a remnant of the hyomandibular cleft. 
The pectoral fins (Plate 21, fig. 12, pc.f.) are very prominent longitudinal ridges, 
which, owing to their being placed on the surface of the yolk-sac, project in a nearly 
vertical direction: a feature which is also found in many Teleostean embryos with 
large yolk-sacs. 
No traces of the pelvic fins have yet become developed. 
The positions of the permanent dorsal, anal, and caudal fins, as pointed out by 
Agassiz, are now indicated by a deposit of pigment in the embryonic fin. 
In an embryo on the sixth day after hatching, of about 15 millims. in length, of which 
we have also given a figure (Plate 21, fig. 14), the following fresh features deserve 
special notice. 
