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Part III. — Sixteenth Annual Report 



by Cunningham, in the eel, and in the fresh eggs of the angler, the John 

 Dory, the red gurnard, the ling, the catfish, and the topknot, while in 

 sections of the grey gurnard, red gurnard, dory, cat-fish, topknot, 

 and eel the germinal vesicle is surrounded by a zone of vacuoles. 

 Cunningham has shown that the vacuolated condition in mounted 

 sections is owing to the oily matter having been dissolved in the 

 process of preparation ; and he also states that the condition above 

 described is characteristic of eggs which possess one or more oil-globules 

 when mature, a conclusion at which I had also arrived.* It is a very 

 conspicuous feature in the smaller fresh eggs of the catfish {Anarrhichas)j 

 in which, on slight pressure under the cover-glass, the germinal vesicle is 

 seen with a low power to be encircled by a narrow, very dark, almost 

 black, well-defined ring, and in sections the vacuolated appearance is well 

 seen. The condition in the young fresh eggs of the angler is shown in 

 Fig. 10, Plate II., but it will be noticed that in sections of the larger 

 eggs the peri-nuclear vacuolation is not at all obvious. The formation of 

 the oil-globules in the young eggs of the John Dory is represented in 

 Fig. 2, Plate III., and the vacuolation in the older eggs in Figs. 10, 11. 

 Sections prepared from an immature ovary of the angler, hardened in 

 platino-osmic mixture, imbedded in paraffin, and mounted in Canada 

 balsam, still retain traces of the blackened oil. 



The oil-globules around the germinal vesicle in the fresh egg, or the 

 vacuolated condition in the mounted sections, is absent in the following 

 species : — Plaice, common dab, long rough dab, lemon dab, witch, 

 haddock, whiting, bib, flounder, halibut, and saithe — and the mature egg 

 in all these species is destitute of an oil globule. It would thus appear 

 that the examination of the immature ovarian eggs of a species is sufficient 

 to indicate the presence or absence of an oil-globule in the mature egg. 

 The early formation of oily droplets in the cytoplasm around the germinal 

 vesicle, before the yolk deposition commences in the periphery, is of 

 interest. It is probable that the chemical relationship between the 

 protoplasm and the oleaginous matter is closer than that between the 

 protoplasm and the more highly differentiated yolk-spherules. In the 

 retrogressive changes which occur in the protoplasm of the mature egg 

 after death, an early feature is the formation of oily-looking droplets. 

 The oil-globules flow together when the watery fluid enters at maturation, 

 to form usually a single sphere. They have no relation to the floating of 

 the egg, and they probably represent a food substance which is present in 

 another form in the eggs of allied species which do not possess an oil- 

 globule. 



The next feature in the growth of the egg is the formation of the 

 yolk, which begins to appear as a peripheral zone of granules in eggs of 

 about 0*2mm., the size varying a little in the eggs of different species. 

 As the egg grows in size the yolk-spherules become more distinct, 

 and their formation extends inwards to the wall of the germinal 

 vesicle in those forms which do not possess a peri-nuclear zone of 

 oil-globules. In species whose eggs are pelagic the constitution of 

 the yolk-spherules appears to be essentially similar, so far as their 

 microscopic appearance is concerned. They are of very different sizes in 

 the same egg, and may range from about 0*02 mm. in diameter in the 

 large eggs of the plaice down to extremely minute granules. The larger 

 spheres appear to be vesicular, with finely granular fluid contents ; some, 



* The presence of numerous peri-nuclear oil-globules in the ovarian egg of the 

 common eel points to the existence of one or more oil-globules in the mature egg. It 

 would therefore appear that Grassi's identification of Raffaele's undetermined species 

 No. 10, which is devoid of oil-globules, with Angwlla vvlgaris, is very doubtful. {Vide 

 Quart. Jo7irn. Mt'cr. Scl, Vol. Z9, Pari 3, p. 382.) 



