DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 733 
primary ‘‘ Urnierengange” communicated with it (No. 88). Hrnneauy also speaks of a 
cellular wall, but it appears to be more truly a wall of clear protoplasm in which nuclei 
rapidly develop, and not wholly a wall of cylindrical cells. In regard to form, it may be 
more or less spherical (kv, Pl. XXII. figs. 8, 9), or markedly ellipsoidal (Pl. XXIL. fig. 12), 
this latter figure being frequently altered by the flattening of its floor (kv, Pl. ILL. figs. 
21, 22) and the increased curvature of the roof,—changes best seen in side views; while 
again its shape may be wholly irregular (PI. III. fig. 14); or lastly, it may simply take the 
form of a sub-embryonic fissure. Secondary vesicles are very frequent, and they present 
the same features as the normal vesicle (Pl. XXIII. fig. 9); but may extend all along the 
ventral line almost to the pectoral region. In the gurnard this multiplicity of vesicles 
is often a very striking feature, whether extending along the sub-alimentary region, or 
accumulated together as a prominent cluster of bubble-like structures. A small anterior 
vesicle in addition to the normal one is often seen (PI. III. fig. 20, and Pl. XXIIL. fig. 8), 
and a connecting granular strand, but there is no apparent tendency to amalgamate. 
The diameter of the larger vesicle in an example of Gadus eglefinus was found to be 
‘005 inch, but occasionally, as in Trigla gurnardus (third day), the vesicles which form 
a group may even be five or six times larger than the ordinary vesicle. An embryo 
of G. eglefinus was observed to exhibit one or two small vesicles near the large 
vesicle, and three hours later, the large or normal vesicle and one of the smaller were 
almost free from the embryo, being in fact pressed into the surface of the yolk. 
Other three vesicles had developed and occupied the region whence the large vesicle was 
protruded, and shortly after, on viewing from above, the vesicles were seen to be upon 
one side of the trunk, viz., that to which the tail was bent. Still more remarkable was 
the situation in some examples of G. morrhua, for just before the blastopore closed, 
in addition to the ordinary vesicle, a large clear vesicle also occurred midway along 
the trunk, and it deeply indented the yolk. Moreover, a vesicle also appeared at the tip 
of certain protoplasmic pseudopodia which were pushed out from beneath the embryonic 
trunk. In another example, Kupffer’s vesicle was situated posterior to the caudal termina- 
tion upon a process of protoplasm. AGassiz and WHITMAN called attention to appearances 
similar to the foregoing (No. 2, p. 73), designating them “ secondary caudal vesicles,” 
and observing that they differed little if at all from Kupffer's vesicle. Whatever signifi- 
cance be attributed to this latter structure, it is in any case simply a fissure or cavity 
beneath the embryo (see section kv, Pl. IV. fig. 5b), and is defined usually by the dorsal 
hypoblast, hy, above, and the periblastic matrix, per, below. Its contents are usually 
homogeneous and clear, evidently a translucent plasma, though occasionally granules 
find their way from the basal portion of the vesicle into its lumen. Such being its 
structure, it is not remarkable that it should vary in shape, or often be a compound 
instead of a single vesicle. Batrour (No. 11, p. 61), RaAvBER (No. 133), and Bavsrant 
(No. 9) favour the view that it is of ancestral value, and represents the invaginated 
enteric cavity of Cyclostomes and Amphibians.* Hrnnecuy could not make out any 
* See also a discussion on the subject by J. T. Cunnincuam (Quart. Jour, Mier. Sci., January 1885). 
