696 PROFESSOR W. C. MINTOSH 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, Gerse believes that, by the contraction of the vitellus, this 
“zone of separation ” is produced (No. 57, p. 330). Keser 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. Kuprrer 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—LeEresouL.er indeed affirming that in Perca 
fluviatilis the egg-contents remain unmoved, and at no time show the intra-capsular move- 
ments so remarkably distinct in Hsox (No. 93, p. 503). He further says—‘ TI have not 
seen it (the rotatory movement) in the white fishes, of which I have observed many species, 
and M. Voer 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, “ exeree un mouvement de 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 
Esow, 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. BamBrke, in Leuciscus (2), described the same change of shape, and speaks 
of the opening (the blastopore, or trow vitellaire of C. Voer) as resembling the mouth of 
* Ransom says the pole at which the movements commence is that resting on, 7.c., in contact with, the capsule ; but 
this can hardly be so. 
