132 



Part III. — Sixteenth Annual Report 



The eggs are so resistant that very considerable pressure is required to 

 rupture them, behaving in this respect like most thick-sheUed demersal 

 ova, and differing from all pelagic. The larger eggs sank at once in sea- 

 water of specific gravity 26*7 (temperature 12'6° C). After shaking the 

 eggs in a 2 per cent, solution of common salt the position of the ger- 

 minal vesicle was indicated by a lighter circular area in the centre ; it 

 may also be shown by pressure, but not until the egg is considerably 

 flattened. 



The follicular investment of these eggs is thick, and so tough and 

 elastic, that after the zona had been ruptured by pressure it allowed the 

 yolk to bulge it outwards, and to strip it in some cases almost entirely 

 from the capsule. The dense follicle is also a point in which the ovarian 

 eggs of Zeus faher differ from ovarian eggs that become pelagic. The 

 flattened capsule had a thickness of 0*058mm. in these half -grown eggs, 

 and the double layer of which it is composed was well marked. It is 

 shown in section in Plate III., figs. 10, 11. 



It is, however, in the yolk that the demersal character of these eggs is 

 perhaps most apparent. The yolk does not flow from a rupture in the 

 capsule in the fluid manner that it does in the opaque stage of pelagic 

 eggs \ it escapes from a small orifice as a coherent column or 

 ribband, only semi-fluid or jelly-like, and it consists of a protoplasmic 

 matrix, in which solid-looking bodies are imbedded. These bodies are 

 the yolk-spherules, which in the fresh condition are not all spherical, but 

 as a rule somewhat irregular in shape. The larger ones measure from 

 about 0*04 to even 0"10mm., and they take on a deep stain (Plate III., 

 fig. 10). With a moderately high power two forms of small spherules 

 can be distinguished — (1) oily-looking and refringent, showing optical 

 concentric lamination ; (2) true yolk-spherules, not very refringent, and 

 full of minute dark, almost black, granules. In mounted sections they 

 appear like mulberries. Besides these, numerous larger oil- globules are 

 contained in the cytoplasm. 



The opaque yolked eggs ranged in size from the large ones described 

 down to about 0'35mm.; smaller ova, destitute of yolk, were present in 

 considerable numbers, and others in which the deposition of yolk at the 

 periphery had just begun (fig. 9, Plate III.). Before any yolk is formed oil- 

 globules appear for the most part in the protoplasm immediately around 

 the germinal visicle, which is thus obscured ; this condition may be 

 observed in eggs as small as 0*1 6mm., in which an envelope, or zona, is 

 formed (fig. 2, Plate III.). By pressure under the cover-glass the dark 

 ring or shell of oil-globules may be made to travel with the germinal 

 vesicle towards a rupture in the capsule, where they become detached in 

 little clusters and escape. In mounted sections prepared in the ordinary 

 way the oil-globules are dissolved, their position being indicated by 

 empty spaces (figs. 9, 10, 11, Plate III.). Thus the germinal vesicle 

 appears to be surrounded in such sections by a vacuolated zone. 



The germinal vesicle exhibits the usual characters found in the ovarian 

 egg of Teleosteans. The nucleoli are conspicuous and highly stained, 

 some of them showing a central brighter area or vacuole (fig. 12, Plate 

 III.). In some cases the central part of the germinal vesicle contains 

 chains of minute stained spherules, or chromosomes, resembling those 

 seen in the advanced eggs of the angler (see p. 103, Plate III., figs. 12, 14). 



Sections were made of the ovary of another fish, 20J inches in length, 

 caught on 22nd July. In this specimen the eggs are not so far advanced, 

 the larger being about 0*45mm., and numerous old follicles, like those 

 described by Cunningham in the ovaries of the plaice and gurnard,* 

 were present. 



♦ QiiaH. Joum. Micr. Sci., Vol. xl., p. 114, 1897. 



