DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 679 
harengus, two separate layers, an outer vitelline membrane, and an inner zona radiata, 
may be distinguished (No. 87, p. 178); but Horrman does not think the distinction 
justifiable—one membrane alone being present, which, however, presents an inner less- 
defined part, probably more recently formed, or in course of formation, from the vitelline 
cortex ; and G. Brook supports this interpretation (No. 34a, p. 201).* Ifthe outer con- 
centrically-laminated stratum be regarded as a layer separate from the inner stratum 
which shows radial striations, then with Kuprrer we must consider the former as of 
exceptional occurrence amongst Teleosteans (No. 87, p. 178). Brock, again, figures two 
Teleostean ova with double capsules, the outer layer being striated in one case and 
unstriated in the other (No. 29, Taf. xxviii. fig. 7, fi; Taf. xxix. fig. 6, b, e). The 
interpretation as a single layer, we repeat, seems, however, better founded, for if the ovum 
of Callionymus lyra be examined, we find external to the zona radiata, which has the 
usual structure, “a series, for the most part, of hexagonal reticulations like those of a 
honeycomb,” not unlike the reticulation of the early ovum of Ammodytes tobianus. 
“These spaces are not quite uniform in size, but many are. Some again have four, six, 
or seven sides; . . . . the septa bounding the reticulations stand out very distinctly, and 
their edges show minute striz ” (No. 106, p. 481, also Pl. xiii. figs. 1,2, 3,4). The ripe ova 
of this species have been examined at the Marine Laboratory, and the reticulation in 
both cases is external, and is evidently inseparable from the zona radiata. The same 
condition would appear to be present in the pelagic ova of Crenilabrus tinca, recently 
described by J. H. List, the outer part of the zona consisting of regular six-sided 
areas, and the inner only of fine parallel striations.t Such elaborate modifications 
of this single layer are probably illustrated by the ovum of Cyprinus dolbula, with 
its radially directed rod-like processes; of Perca fluviatilis (No. 111, p. 186), with 
its prominent hollow cylindrical appendages, which interlace, and, with the mucous 
envelope, hold the eggs together in “élégants réseaux,” as LEREBOULLET describes 
(No. 93, p. 471); but they do not serve, as the same author states, for absorption 
like the minute canals, though both structures penetrate the capsule. In such forms also as 
Blennius, Gobius, and pelagic eggs like Heliasis and Belone, long filaments occur near the 
micropyle, and are pronounced by Horrman, who describes them, as simply excrescences 
of the zona radiata. If we regard the capsule in Teleosteans as essentially a single layer, 
then the dissimilarity of the elaborately modified capsules of the foregoing species 
—of the less complex capsule in Clupea harengus (No. 87, p. 178), and in sow Lucius 
(No. 93, p. 465); and of the extremely simple membrane in the ova of Gadoids, Pleuro- 
nectide, and others, wholly disappears. The species in which various layers, not to 
say distinct membranes, have been described, find their place in the same category as the 
ova of the cod and like forms with simple layers. That the capsule can undergo elaborate 
modification is easily understood, when it is noted that in its early condition it is always 
* See also LeREBOULLET's description of a similar inner layer closely applied to the yolk in the pike, the outer 
stratum being alone striated (No. 93, p. 465). 
+ Zeitsch. f. wiss. Zool., Ba, xlv. (1887) p. 596, tig. 1, a, b. 
