14. A. A. W. HUBRECHT. 
In Tarsius on the other hand, where in an overwhelming 
number of cases the embryonic shield undergoes the changes 
consequent upon the first appearance of notochord and somites 
without any faint trace of a blastopore, one quite 
exceptional case came under observation (Fig. 52) in which — 
what was evidently an atavistic attempt in that direction was 
noticed; all the more important because it helps us to fix the 
spot in the didermic gastrula at which the blastopore n aturally 
oecurs. Similarly blastoporic openings, or attempts at such 
a perforation in these early stages, have been noticed in the 
rabbit by Keibel (’89; Figs. 46, 47), in the mole by Heape 
(Fig. 54), in the opossum by Selenka (Fig. 55), in the shrew 
by myself (Figs. 56 and 57). In the diagrams a few of these 
observations have been reproduced. 
The gastrula stage and the blastopore of the mammalia are 
thus limited to the early phases and the simple phenomena 
here described. The blastopore becomes closed in all the 
eases above noticed, and after that a series of processes are 
initiated in which it would be \utterly misleading further to 
use the word blastopore, Gastrulamund, Urmund, or Urmund- 
lippen. ‘These structures im the further development that 
have been thus termed ought to be termed differently if we 
wish to put an end to the confusion that obscures these 
points at the present moment. 
At the same time it should be noticed that one of the first 
features by which the formation of the notochord begins, 
viz., the formation on the embryonic shield of that median 
ectodermal proliferation, which I have called (’90) the 
protochordal wedge (Primitivknoten, Bonnet = Hensen’scher 
Knoten), takes place in the identical spot where the evanescent 
blastopore was or is situated (Fig. 52); and that from this point 
backwards a median region of proliferation extends which 
on O. Hertwig’s example has been called the homologue of 
the ‘“Urmund” and the ‘‘ Urmundlippen,” but which we 
ought to compare as I have elsewhere advocated (’02, 705) 
with an elongated stomodeal slit, which even in the hypo- 
thetical ancestral forms was no longer a blastopore, but 
