258 EXPERIMENTS AND OBSERVATIONS 
jaws. But many of the characters of the sub-family cannot definitely 
be proved to be adaptive, e.g. the narrow symmetrical pelvic fins 
and the slight anterior extension of the dorsal fin. 
II. Tar Devetopment or tHE Kao Iw Fuar Fishes AND PIPE-FISHES. 
Since my paper in Vol. III, No. 2, p. 154, of this Journal was 
written I have been continuing my studies of the development of 
the eges in the ovaries of fishes. My attention has been given 
principally to the history of a definite body in the yolk known as 
the vitelline nucleus, but quite distinct from the proper nucleus of 
the eve or germinal vesicle. I hope to be able at some future time 
to publish a full account of my observations with adequate illus- 
tration, but in the meantime some account of the subject in the 
Journal of the Association may be useful. 
In the fresh state it is almost impossible to perceive any trace of 
the vitelline nucleus, only a faint indication of it can be made out 
after famiharity with it has been gained by the study of its struc- 
ture in preparations which have been subjected to the action of 
reagents. In fishes in which the eggs before the development of 
yolk are extremely transparent the structure can be easily seen 
after treatment with dilute acetic acid, in a small portion of the 
ovary simply spread out ona slide. In those eggs in which the 
development of yolk has made considerable progress the body in 
question can only be seen in prepared sections. In a piece of the 
ovary of a flat-fish in which there is no yolk—for instance, a flounder 
or plaice,—on the addition of acetic acid the transparent protoplasm 
of the ege gradually coagulates, and the first change to occur is the 
appearance of the vitelline body as a spot which is more opaque 
than the surrounding substance. In the larger ova (Fig. 1, b) this 
body is round and of considerable size, somewhat larger than one 
of the nucleoli of the germinal vesicle, and it is situated between 
the germinal vesicle and the surface of the ovum. Examined with 
a high power it is seen to consist of a spherical collection of 
minute granules. In the smaller eggs (Fig. 1, a) those about *118 
mm. in diameter, the vitelline nucleus is somewhat smaller and 
close to the surface of the germinal vesicle. In still smaller eggs, 
only ‘10 mm. in diameter, the body can just be discerned as a 
few granules just outside the membrane of the germinal vesicle, and 
in ova smaller than this no trace of it is visible. I have not been 
able to see any indication that the vitelline body is situated on a 
particular side of the egg. ‘The egg is approximately spherical ; the 
