DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 803 
on each side of the thoracic region, extending dorsally and ventrally, forming in fact two 
halves of the pectoral girdle as yet disjoined below. RypeEr distinguishes, before the 
development of the cartilaginous girdle, an oblique pectoral fold (No. 141, p. 520), con- 
sisting of a band of mesoblast, out of which, he states, the girdle develops. There 
appears on each side, therefore, a clear yellowish rod, tapering at its upper and lower 
extremities, and curved like an //—as in the gurnard on the eighteenth day (cl, Pl. X. 
figs. 2, 3; also Pl. XIII. figs. 5, 6, 7). In- Pl. XI. fig. 18, this bar is figured as removed 
from a larval Pleuronectid about three weeks old. The species was not determined. The 
small triangular element attached, though not unlike the post-temporal, is probably the 
coracoid bone. This secondary bar may be readily recognised by its form and position 
as the clavicular element (c/), and it develops in certain species, as in the gurnard, 
the Gadoids, and others, without being preceded by a bar of cartilage-cells, and in these 
forms the basal part of the fin-cartilage is greatly developed, as if preparatory to inclusion 
as a posterior part of the girdle. If the homogeneous, translucent, brittle rod, strongly 
suggestive of chitin, be the clavicle, then the elements behind, which become attached to 
it, must be the scapular and coracoidal portions of the permanent girdle. By the 
breaking-up of the basal portion of the cartilaginous fin-plate the system of basilar 
pieces is formed (Pl. XVII. fig. 5). Kinestey and Conn speak of this proximal car- 
tilaginous thickening as parallel to the axis of the trunk, and as preceding the distal 
rays. ‘This basal skeleton,” they say (No. 78, p. 210), “instead of appearing as a pair 
of rods as described by Ryprer, was rather a broad plate with a central opening, as if 
his rods had united at their extremities.” The same feature was also seen in Loplhius. 
There is much obscurity in regard to the development of the ultimate elements of the 
paired fins, and their relation to the axial girdles. The details of this further develop- 
ment, with the theoretical considerations involved in their interpretation, have been 
dealt with by one of us in a special paper.* 
Ventral Fins.—The development of the ventrals will be alluded to when describing 
the post-larval stages (vide Pl. IX. figs. 2,3; and Pl. XVIII. fig. 3). They are late in 
making their appearance in the pelagic forms. 
X. Mernops AnD TECHNIQUE. 
I. MernHops.—The ova and embryos are treated according to the usual methods of killing, 
fixing, staining, and cutting. Notwithstanding the large number of methods recommended by 
various embryologists, the ova and early embryos of Teleosteans may still be counted amongst the 
most difficult objects subjected to the microtomist’s processes. The recommendations of various 
investigators are most conflicting, and a perfectly efficient and reliable killing, staining, and 
imbedding process continues to be a desideratum. WuiTMAN, after trial of the usual hardening 
agents, “failed to find any completely satisfactory method of preserving the vitellus; even the 
germinal dise cannot well be preserved by any of the ordinary hardening fluids ” (No. 159a, p. 152), 
and this agrees with the common experience of investigators. 
* E. E. Prixce “On the Development and Morphology of the Limbs of the Teleosts,” Elizabeth Thompson 
Fund, U.S.A. 
