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 larvae 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 



