128 BULLETIN OF THE 
already pointed out for Fundulus (p. 126). My observations on the 
Shad (Clupea sapidissima) and the Cod (Gadus morrhua) also confirm 
this point for other Osseous Fishes besides Fundulus, and I believe 
that this condition is typical, if not constant, in the entire group of 
Fishes. 
As I have already stated (p. 96), Oellacher traced the origin of the 
pectoral fin from the mesoderm. He did not, however, believe simply 
in the priority of the mesodermal modification, for he supposed an ecto- 
dermal fold to be absent in the case of the pectoral fin in the Trout. He 
evidently saw the pectoral plate at a stage prior to the ectodermal mod- 
ification,— a stage presumably corresponding to Figure 41 (Plate VI.) of 
Fundulus, —but he did not discover that subsequently an ectodermal 
fold is developed; hence his observation did not reveal the error of 
Balfour and others, who assumed that the ectodermal fold is the first 
step in the development of the pectoral fin. 
I am unable to make any comparison between the condition of the 
unpaired fins in Fierasfer and my own observations in Fundulus, as 
I have discovered no structure in the pectoral fin of Fundulus com- 
parable to the homogeneous stratum which has been observed by Emery, 
and is regarded by him as partly mesodermal and partly ectodermal in 
origin. 
The extreme view held by Prince (’86, p. 697), that the pectoral fins 
of Osseous Fishes are of ectodermal origin, and are differentiations of a 
continuous lateral expansion of the epiblast, seems to me to be based 
more upon theoretical considerations than upon observed facts. The 
only way in which I can account for the author’s description is to 
assume that his “two epiblastic lamellee (separated by a fissure) lying 
flat upon the vitellus,” which he regards as the beginning of the pec- 
toral fin, are really the primitive embryonic layers, either including the 
three at an early stage (compare Fig. 5 in Fundulus) before their com- 
plete differentiation, or including only ectoderm and mesoderm at a 
later stage (compare Fig. 26 in Fundulus). Indeed, more recently a 
similar belief is defended by M’Intosh and Prince (’90, pp. 800-803) 
in their joint paper on the development of Teleosts. In this paper the 
ground taken is still more peculiar, and the interpretation is much 
involved in speculation. 
I have already quoted at some length the views of these authors 
(pp. 98, 99), and need here only recall the fact that they regard the 
lateral margin of the blastoderm at an early stage, virtually before the 
complete differentiation of the primitive layers, as the beginning of 
