DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 879 
in Pl. XXL. fig. 3, a feature probably due to position under examination. The relation of 
the large globule to the position of the respective larvee when at the bottom of the water 
is not perfectly clear, though there is reason to believe that, in Anarrhichas, as already 
pointed out, it is directly connected with the attitude assumed by the larva when at rest. 
Young salmon lie on one side amongst the gravel in their early stages, or occasionally 
rest with the yolk-mass dipping between the pebbles on the bottom, so that a definite 
position of the oil-globules in front would appear to be of little importance. The 
contained fluid, or deutoplasm, of the yolk-sac seems to be similar in both species. 
When discharged into the water it is transparent, viscous, and very tenacious. After a 
time it becomes solid, and of an opaque white hue like a stratum of tallow. In the sal- 
mon it presents in the latter condition abundance of dense oily globules, with adherent 
granules, resembling nucleated cells. In the large globules, however, the granules form 
only a superficial fringe. In some cases the oily matter, on escaping, sinks to the bottom of 
the water. Two kinds, indeed, of this matter are present—(1) orange-tinted oil, which 
floats at the surface, and (2) minute particles of oil imbedded in and held down by 
granular substance. When pressure is applied to the large globule it divides into two 
or more portions, so that it would appear that no definite protoplasmic investment 
encircles it. It also occasionally passes to the fundus (Pl. XXII. fig. 7), and sometimes 
its surface is slighted fissured. Some of the oil-globules appear paler in colour than 
others of the same size. The large globule is observed to persist almost till the 
posterior process disappears from the yolk-sac (Pl. XXII. fig. 9). Externally the latter in 
the salmon is covered by a layer of nucleated tesselated epithelium, the nuclei having 
nucleoli, and beneath is a fibrillated coat, below which the vascular layer lies. In hernia 
of the yolk-sac, the free portion presents a striated appearance, due possibly to the 
protrusion of the vascular (yolk-hypoblast) through the non-vascular layer, for in one 
example blood-vessels proceeded quite up to the margin of the hernia. 
The walls are contractile, for the sac shrinks towards the body of the embryo on the 
escape of the contents. So also the walls contract during the gradual absorption of the 
contents of the sac, as observed at the end of the first week (Pl. XXII. fig. 6). As the 
organ shrinks, obliteration of the smaller and then closure of the larger vessels takes 
places. By and by (about the 13th day) the anterior region of the sac becomes flattened, 
so that it forms merely a slight swelling on the surface ; and sometimes a few carunculi 
appear at the fundus. At the end of the third week the vitelline vein as well as the 
yolk-sac is much diminished. About the end of the fifth week the latter forms only an 
abdominal swelling, and is streaked with bars of pigment, which are directed downward 
and backward. 
A glance at the figures of the sac during its later stages in Anarrhichas will show 
that the absorption takes place in a different manner from that just detailed, since in- 
stead of the final prominence being posterior as in the salmon, it is in Anarrhichas 
anterior, and the large oil-globule in the latter likewise is in the same region. 
In regard to the circulation in the yolk-sac, the great vitelline vein in the salmon is 
