732 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
J. T. Cunntncuam. Again, it is observed that towards the closure of the blastopore the 
“limbs” of the blastoderm seem to go—so far—into the embryo. When this projection is 
less marked the caudal end of the embryo may still destroy the regularity of the 
circumference, as in Pl, III. fig. 23, recalling the horse-shoe-shaped blastopore of Astacus, 
such variations being easily explained by the bulk of the contained deutoplasmic matrix 
and the tension of the blastodermic membrane. This pressure outwards, as VAN BAMBEKE 
pointed out, and the restraint of the blastoderm, frequently produce a contracted opening, 
like the mouth of a balloon (see Van BamBeke’s figure, No. 20a, pl. ii. fig. 9), from 
which a plug of yolk protrudes, just as in the Crustacean ovum, mentioned above, an 
endodermal protrusion fills up the blastopore. In Teleosteans, as in Astacus, the plug 
diminishes as the blastopore closes. In the gurnard, as the blastopore closes, projecting 
cells are seen, which often send out protoplasmic processes, those protruding from the 
blastoporic lip somewhat resembling the processes which under pressure are pushed out 
from the marginal cells of the blastodermic ring at an earlier stage (PI. II. fig. 16). The 
time of the closure of the blastopore of course varies, according to circumstances, in 
common with the other features of development. Thus in Trigla gurnardus the closure 
was observed to be effected on the third day after fertilisation; whereas in another series 
earlier in the same season (May), the temperature being lower, this did not occur until 
the fifth day. As closure takes place the yolk may often, in side views, be seen still to 
project as a diminished yolk-plug (Pl. IIL fig. 15); but usually as closure is effected 
the blastopore forms a trumpet-shaped opening, round which the deeply corrugated lip 
rises as a circular eminence (PI. III. figs. 9, 10, 21). 
Kupfjer’s Vesicle-—When the blastopore closes, or often a few hours earlier,* a minute 
vesicle arises on the ventral aspect of the embryo slightly anterior to the caudal termina- 
tion. Its advent is preceded by the appearance, in some cases, of vesicles or small 
elongated spaces (PI. III. fig. 17), evidently filled with colourless or pinkish fluid. They 
occur quite at the margin, as if the advancing embryonic area became elevated at these 
points, and progressed over them. In other cases a granular thickening occurs in which 
a few rounded vesicles are imbedded, as can be readily seen in Trigla gurnardus and 
other forms shortly before the blastopore closes. K1in@stey and Conn noted such a group 
of minute vesicles, which in five hours apparently by coalescence showed the characteristic 
form and appearance of Kupffer’s vesicle. It is defined in their figure, above by hypo- 
blast, and below by periblast (No. 78, pl. xvi. fig. 54). It is variable in the precise time 
of its appearance, for Hennecuy noticed it in Salmo fario when only about half of the 
vitellus was covered by the blastoderm (No. 80). In Molva vulgaris, Gadus morrhua, 
and other species it is usually not visible during the open state of the blastopore, but 
both in position and time of its appearance it varies, though the clear vesicular structures, 
with a delicate envelope, are usually exhibited. Kuprrer, who first described it in 
Crastrosteus, Gobius, and others, calls it the “allantois,” and says that it acquires a coating 
of cylindrical epithelium, and finally becomes the bladder, though he did not show how the 
* J. T. Cunsrycuam found that in Clupea it was late in appearing (January 1886). 
