222 
In Amphioxus, on the contrary, we may expect the animal 
pole at the same place as in Annelids, i. e. on the anterior 
surface of the prostomium, a good distance in front of the 
neuropore. This also is confirmed by the facts. In Amphioxus, 
it is true, we cannot trace the fate of the animal pole with 
such certainty as in worms and molluscs, the cleavage 
being of the indeterminate type which soon renders it 
impossible to distinguish the individual cells from each 
other and to determinate from their arrangement the place 
of the animal pole. The polar bodies, however, often 
remain attached to the developing egg for a considerable 
time, up to the gastrula-stage. One of these eggs, as obser- 
ved by CERFONTAINE (1906), is reproduced here in fig. 12. 
if we compare ars 
cEPRLRAPAAA stage with that of fig 
eslpl nde it will be evident at 
Ee MS once that, if it might 
be possible to observe 
the polar bodies in the 
latter stage, they would 
be found on the surface 
of the prostomium at a 
considerable distance 
in front of the neuro- 
ore. Thus for the 
Fig. 12 rider of Amphioxus, third time we reach 
ster CeRFONTAINE, 1906 the same conclusion, 
viz: that the fore-brain 
of Craniates is a new acquisition with reference to the 
Acrania. 
HATSCHEK'’s view on the Craniate brain. — A similar 
assumption, combined with the view that the infundibulum 
represents the primitive fore-end of the brain, comparable 
to the neuropore of Amphioxus, has, anticipated already by 
Vv. BAER's investigations, found several adherents and 
has recently been defended by HATSCHEK (1909. p. 497). 
The praechordal part of the brain is imagined by them 
to be a secondary outgrowth from the epichordal part as 
found in Amphioxus (cf. the quotation from WIEDERSHEIM 
anon). According to my theory, however, there is no question 
of a forward outgrowth of the original ‘epichordal brain of 
Amphioxus but of a forward extension and an incorporation 
of ectoderm in front of it. 
