DEVELOPMENT AND LIFE- HISTORIES OF TELEOSTEAN FISHES. 733 



primary " Urnierengange " communicated with it (No. 88). Henneguy 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 XXIII. figs. 8, 9), or markedly ellipsoidal (PI. XXII. fig. 12), 

 this latter figure being frequently altered by the flattening of its floor (kv, PI. III. 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 (PI. 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 PI. XXIII. 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 ceglefinus 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. ceglefinus 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, PI. IV. fig. 56), 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. Balfour (No. 11, p. 61), Rauber (No. 133), and Balbiani 

 (No. 9) favour the view that it is of ancestral value, and represents the invaginated 

 enteric cavity of Cyclostomes and Amphibians.* Henneguy could not make out any 



* See also a discussion on the subject by J. T. Cunningham (Quart. Jour. Micr. Sci., January 1885). 



