DEVELOPMENT AND LIFE-HISTOEIES OE TELEOSTEAN FISHES. 679 



harengus, two separate layers, an outer vitelline membrane, and an inner zona radiata, 

 maybe distinguished (No. 87, p. 178); but Hoffman 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).* If the outer con- 

 centrically-laminated stratum be regarded as a layer separate from the inner stratum 

 which shows radial striations, then with Kupffer 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, f. ; 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 striae " (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 tinea, 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 jiuviatilis (No. Ill, p. 186), with 

 its prominent hollow cylindrical appendages, which interlace, and, with the mucous 

 envelope, hold the eggs together in " elegants reseaux," 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 Hoffman, 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 JEsox lucius 

 (No. 93, p. 465); and of the extremely simple membrane in the ova of Gadoids, Pleuro- 

 nectidse, 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). 



t Zeitsch.f. wiss. Zool., Bd. xlv. (1887) p. 596, tig. 1, a, b. 



