DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 695 
Especially is this the case in ova which show a preformed discus proligerus. In the pike, 
for instance, LEREBOULLET states that both are alike, save in the formation of a “ disque 
huileux” which collects in the fertilised egg, as GeRBr also describes in the egg of the 
trout, two hours after fertilisation, the circular germinal area appearing as if enclosed 
in a “crown of oil-globules” (No. 57, p. 330); yet even this feature may appear in the 
unimpregnated egg, and it cannot therefore, as LEREBOULLET confesses, be traced to the 
action of the sperm (vide No. 93, p. 478). The fertilised ovum in pelagic forms (e.g., cod 
and gurnard) is more readily distinguished, as the segregation of the protoplasm is plainly 
visible within an hour or two after fertilisation; but the transference is not to the upper 
pole, as in a large number of demersal forms, but to the lower pole, where the patera or 
flattened disc is formed of clear, straw-tinted protoplasm containing minute spherules, 
which are especially numerous at the base and periphery. During the process of segrega- 
tion the contour of the vitellus becomes very distinctly corrugated—an appearance pro- 
duced by the streaming of the protoplasm along definite meridional lines; and pelagic 
forms are especially favourable for observing this polar transference. Ransom, in common 
with other observers, wholly failed to detect this movement (No. 127, p. 458), though he 
says that the granules often form radial lines round the margin of the concentrating dise 
(Ibid., p. 459). Besides passing along the superficial areas, much protoplasm probably 
also glides in the deeper strata of the vitellus to the base of the germ during the first 
hour after entrance of the sperm. Such streaming of the protoplasm towards the disc has 
been noted by many observers, and recently Kowatewsky has described it in Carassius, 
Polyacanthus, and Gobius (No. 86). In two hours or more, according to the temperature 
and other conditions, a plano-convex disc is formed, composed of an almost homogeneous 
matrix. The dise in the fertilised ovum is always well defined and prominent, and 
continues to receive additions of protoplasm, so that it increases in size, and becomes more 
pronounced; whereas in the unfertilised ovum, when a disc is formed, it becomes “ vague, 
irregular in outline, and loses coherency” (No. 57, p. 330). The primary segmentation- 
nucleus has rarely been detected in the blastodise before cleavage, granules and colourless 
vesicles alone appearing in its matrix. The breathing chamber gradually becomes more 
distinct; but this may also happen in the unfertilised condition, as Ransom found that such 
ova may, after being in contact with water for an hour, show this marked interspace. Its 
formation, as well as the concentration of the disc, Ransom holds to be only indirectly 
due to the spermatozoa, which may render more easy and rapid the influx of the 
surrounding medium into the egg (No. 127, p. 463). The same observer carefully studied 
the formation of this space in Gastrosteus, and states that it first appears close to the 
micropyle, whence it “ gradually extends over the rest of the yolk-ball, being complete in 
three to five minutes after the spermatozooids have been applied” (Jbid., p. 457); but ina 
note at the foot of the page he says that water may enter more freely, and the chamber 
arise simultaneously in the ova of other fishes. Newport, who was the first to signalise 
this perivitelline space, speaks of it as “ respiratory,” and being in Rana “‘at first but a 
small area” (No. 112, p. 187), a view coinciding with Ransom’s upon the same ovum, for 
