264 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
the total abseuce of intermediate forms between the gastrula and that of Amphioxus, 
and seeond that the theory leads us nowhere ; it does not admit of any exact com- 
parison between the teleostean embryo and those of other vertebrates. 
Kupffer’s theory of gastriilation (25, 26) is very different, but stands in complete 
opposition to tlie facts. According ro Kupffer the vesicle, which bears his name, arises 
by an invagination from the ectodermal surface, and alone represents the AmpMoxus 
invagination. The functional entoderm is derived from the yolk and is regarded as a 
structure which has gradually replaced the invagiuate entoderm. 
p.tv 
-P 
an. v.JTi. 
Fig. 10.— Diagram of Teleost gastrula, not long before blastopore closure — d. 1. (p.p.), dor- 
sal lips (post, pole) of blastopore ; v. 1. (a.p.), ventral lip (ant. pole) of blastopore; k. v., 
Kuiiffer’s vesicle; arch., arcbenteron ; p. 7i., prim, hypoblast; ec., ectoderm ; jj., peri- 
blast; e. e. g. r. {v. mes.), extr.a-embryouic germ ring (ventral mesoderm); y, yolk; an. 
V. m., extent of tract of ventral mesoderm in ancestor. 
Kollmann (29) entertains the strange and difficult view that the discopore {disc., Fig. 
9) is the blastopore. His theory has already been criticised by Ryder (35, j). 493), 
with whose objections I agree. There is really nothing to support the theory ; the 
generalized diagram of the meroblastic gastrula, which Kollmann gives, is a very differ- 
ent form from the Teleost embryo, and an acceptance of his homology of the discopore 
with the blastopore makes it impossible to understand any part of the further devel- 
opment. The closure of the blastoderm edge at the tail end of the embryo becomes 
incomprehensible, while the position of the “ blastopore ” (discopore) lip directly under 
the head of the embryo (when compared with its position in AmpMoxus), and the fact 
that the “blastopore” (discopore) never closes, remain absolute mysteries. 
To Ziegler (48) is due the credit of having first instituted a detailed comparison 
between the teleostean and Amphibian gastrulas, for it is only through such a com- 
parison that the intricacies of the fish development become comprehensible. Ziegler’s 
