DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 685 



spheres are embedded.* During the first hour after fertilisation these translucent vesicles 

 are readily seen under a moderate power (450). Occasionally granular protoplasm is 

 observed at certain parts of the contour of the vitellus in the haddock. A similar appear- 

 ance occurs in the cod, in ova which are abnormal though still translucent. Amongst 

 these vesicles are others extremely minute and very numerous, which in refracted light 

 have the appearance of punctures. 



To distinguish the albuminoid matrix, which forms the greater part of the bulk of the 

 egg, from the active germinal protoplasm, the name " deutoplasm," conferred by Prof. 

 E. van Beneden, is both appropriate and convenient. This deutoplasm rarely has the 

 appearance of yolk-segments contained in a sponge-like network ; but is composed in 

 many pelagic eggs of minute yolk-particles aggregated in a matrix apparently homo- 

 geneous, highly refractive, and coagulating on the addition of water. The latter feature 

 has long been known, for Lereboullet found coagulation to take place in the ovum of 

 Salmo fa rio, just as Vogt had noted in Coregonus palcea (No. 155, p. ll).t Broadly 

 speaking, we may say of the yolk in the Teleostean ovum that it possesses special features 

 of its own, which separate it from the nutritive matter of other vertebrates ; whereas the 

 yolk of the Elasmobranchii resembles in a very marked manner that in the Avian egg. 

 There is apparently little difference in the specific gravity in various parts of the deuto- 

 plasmic matrix, as it retains any position in which it is placed before the aggregation of a 

 polar disc ; but Ransom questions whether its specific gravity is equal throughout, and 

 thought that nearer the surface it is of a more fluid consistency, or, as he says, " I had 

 some reason to think a little less dense than the centre, as it ran more freely ; but all parts 

 flowed from a rupture like very thick syrup " (No. 127, p. 436). The greater density of the 

 deeper deutoplasm can be readily explained by the movement of the interfused protoplasm 

 surface-wards, so that the central part of the yolk-globe becomes more purely yolk- 

 matter, while with the more superficial strata a larger, though constantly diminishing, 

 quantity of germinal protoplasm will still be intermingled. Kowalewsky considers that a 

 protoplasmic network must exist in the yolk (Carassius, Poly acanthus, and Gobius), since 

 after hardening the latter presents polygonal partitions (Zeitsch.f w. ZooL, vol. xliii., 1886). 

 He also terms the yolk the entoblast, in contradistinction to the germinal disc or ectoblast. 



The freedom with which the so-called oil-globules in various forms (e.g., the gurnard 

 and ling) move through the deutoplasmic globe not only proves its very fluid consistency, 

 probably corresponding with that of thick cream, but shows the absence of a definite 



* Lereboullet inclines to the opinion that the yolk is active in the formation of germinal protoplasm ; " at any 

 rate," he says, "in the Lizard and Bird we find it before the germinal vesicle is ruptured " (No. 95, p. 11). 



t The behaviour of the deutoplasm under various conditions was made the subject of some interesting observations 

 by Dr Davy in the ovum of the charr (Salmo umbla), and he found that while contact with water in quantity coagu- 

 lated it, the careful application of water in minute portions did not do so. Again, when heated even so high as 212° F., 

 it did not coagulate, nor did it under the influence of steam ; whereas boiling water at once effected the change, owing, 

 it was inferred, not to the heat, but to the admixture of water. While acids, salts, and alkalies had no coagulating 

 influence, except when dilute, nitric acid, corrosive sublimate, and alcohol produced the change immediately. Davy 

 came to the conclusion, as a result of his researches, that the deutoplasm of the charr and other Salmonoids has pro- 

 perties distinct from the albumen of the Avian yolk (No. 50, p. 436). Results similar to those of Davy were obtained 

 by Ransom in the various Teleostean eggs which he studied (No. 127, p. 436). 



