696 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



he believed he saw it arise, just as in Gastrosteus, near the micropyle. Most recent 

 observers, including List, describe this perivitelline space in Teleostean eggs. To 

 what is the formation of this chamber due % Does the vitellus, which before fecundation 

 fills up the intra-capsular area, diminish, or does the external capsule really enlarge ? On 

 the one hand, Ransom maintains that the yolk-sac or capsule enlarges (No. 127, p. 457); 

 while, on the other hand, Gerbe believes that, by the contraction of the vitellus, this 

 " zone of separation " is produced (No. 57, p. 330). Keber has further surmised that part 

 of the contents of the egg may flow out through the micropyle (No. 77), and the egg- 

 mass would thus decrease. Kupffer considers that both the first mentioned phenomena 

 happen, for he says that in Clupea not only does the yolk contract, but the capsule 

 enlarges by as much as one-quarter of its diameter (No. 87, p. 185). A still more 

 marked increase in size Lereboullet noted in the egg of Perca, which, he says, by 

 absorption of water through the radial tubes acquires a volume twice that which it had 

 before extrusion (No. 93, p. 471). Usually, however, the enlargement of the Teleostean 

 ovum is so small as not to be readily noticed. 



Movements of the Yolk. — The curious movements of the vitelline mass, which have 

 been described by many observers, and are stated by Ransom to be " the most striking 

 phenomena which follow on the entrance of the spermatozooids into the egg" (No. 127, 

 p. 463), are not visible in all Teleostean ova. At any rate, if performed at all, they are 

 obscure, or so imperceptible as to have escaped notice in pelagic ova, while in demersal 

 ova they are occasionally not exhibited — Lereboullet indeed affirming that in Perca 

 jluviatilis the egg-contents remain unmoved, and at no time show the intra-capsular move- 

 ments so remarkably distinct in Esox (No. 93, p. 503). He further says — " I have not 

 seen it (the rotatory movement) in the white fishes, of which I have observed many species, 

 and M. Vogt has not noticed it in Coregonus." In addition to the undulations, or 

 " oscillations " as Ransom terms them, which usually pass like a wave of contraction from 

 one pole * to the opposite pole, and occasionally along the equatorial line, producing a 

 dumb-bell outline in the latter case, there are rotations of the vitellus en masse. Ransom 

 did not observe any rotation in Gastrosteus, which exhibits the oscillations very distinctly, 

 nor did he in other ova, though he admits that such movements on the polar axis were 

 not improbable. Lereboullet again speaks of another movement, in fact, a simultaneous 

 double movement: the vitellus, he says, " exerce un mouvementde rotation sur son axe et 

 un mouvement de translation autour de la coque " (No. 93, p. 497). These motions seem 

 to continue during the early progress of cleavage, but cease, according to Lereboullet, when 

 three-quarters of the yolk-surface are enveloped. He describes at this later stage, in 

 Esox, an alteration in the form of the vitellus ; it elongates and becomes pear-shaped, the 

 narrowest diameter circumscribing the part of the yolk not yet covered by the extending 

 blastoderm. Bambeke, in Leuciscus (?), described the same change of shape, and speaks 

 of the opening (the blastopore, or trou vitellaire of C. Vogt) as resembling the mouth of 



* Ransom says the pole at which the movements commence is that resting on, i.e., in contact with, the capsule ; but 

 this can hardly be so. 



