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. Kyder 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 f, — as in the gurnard on the eighteenth day (cl, PL X. 

 figs. 2, 3 ; also PI. XIII. figs. 5, 6, 7). In PI. XL 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 (cl), 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 (PI. XVII. fig. 5). Kingsley 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 Ryder, 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 Lophius. 

 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. Methods and Technique. 



I. Methods. — 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. Whitman, after trial of the usual hardening 

 agents, " failed to find any completely satisfactory method of preserving the vitellus ; even the 

 germinal disc 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. Prince " On the Development and Morphology of the Limbs of the Teleosts," Elizabeth Thompson 

 Fund, U.S.A. 



