Yolk of Teleostean Ova. 89 



gitius*, Tinea vulgaris f, &c. In the salmon the globules 

 are held in position by the coherent granular cortex of the 

 vitellus; they are not, however, merely free vesicles de- 

 fined by the surrounding matrix, but, as His notes, " sind je 

 von einer Hiille protoplasmatischer Substanz umgeben ' ' |. 

 This enveloping coat is well seen in the gurnard, and it in- 

 creases in thickness as development proceeds, being very 

 uneven and imprisoning many small colourless vesicles, pre- 

 cisely as His tigures in the case of the ovum of the salmon 

 &c.§ 



Van Beneden has omitted to show any definite layer, and 

 LerebouUet does not indicate it in the ovum of Perca ||, 

 though it is improbable that in either case the globule is 

 destitute of the limiting layer present in other forms. His 

 figures, in the plates just referred to, connected and isolated 

 globules in the eggs of the salmon, trout, and grayling, and 

 discusses fully the character of the coherent granular proto- 

 plasm which clothes them ^. 



The precise chemical nature of these large globules is still 

 involved in some uncertainty. That they are of an oleaginous 

 nature cannot be doubted, though it is scarcely accurate with 

 E. Van Beneden to describe a sphere of this kind as "a drop 

 of oil or fat," for the investigations of Professors His and 

 Miescher show its composition to be that of no known fat **. 

 If an ovum of the gurnard, for example, be treated with 

 osmic acid, the minute vesicles scattered over the vitellus 

 stain very rapidly and deeply, whereas the large globule is 

 coloured slowly and more faintly — proving the former to be 

 more emphatically oleaginous than the latter. The laro-e 

 globules exhibit a more or less brilliant translucency ; they 

 float in water and are soluble by ether, though, according to 

 Miescher they reveal no more than a trace of phosphorus. 



Their composition, while closely allied, is not identical with 

 that of any of the fats, and they may best be associated with 

 those remarkable derivatives of albumin, the lecithin-group. To 

 that group His, indeed, refers them, though he confesses that 

 strictly their nature is undecided. The association of these 

 spheres with lecithin is a matter of extreme interest, for 

 lecithin is a substance always present in cells of ova under 



* Phil. Trans, vol. clvii. (1867). 



I Van Bambeke, o}). cit. p. 2, and plate i. fig. 2. 



X His, Uutersuch. iiber das Ei und die Entwickl. bei Knoclienfisclaen, 

 1873, p. 7. 



§ Op. cit. Taf. i. figs. 1, 2, 4, 5, 11, and 12, and Taf. iv. fig. 38. 



II LerebouUet, Mem. des. sav. strung, t. xvii. p. 460, and plate iii. 

 figs. 3, 7, and 8. 



^ Op. cit. pp. 6, 7. ** Ihid. p. 7. 



