66 A. As W. HUBRECHT. 
ence of what was the ancestral “ Riickenmund ” of a more 
actinian-like ancestor. 
In a later paper Semon (01, p. 317) retracts his original 
comparison, arguing that the gastrulation process has already 
ceased before the “ Naht” becomes visible. Here again the 
false interpretation of the gastrulation process (see Hubrecht, 
05) has misled Semon, whose original interpretation can be 
adhered to if we substitute notogenesis for gastrulation, and 
dorsal mouth (Riickenmund) for blastopore (Urmund). 
Protochordal plate and protochordal wedge in their mutual 
relations may be considered identical with what we discussed 
for the Amphibia. 
The ventral mesoblast, which, in Petromyzon, does not 
appear as SO distinct a median and early proliferation of the 
ventral lip of the blastopore such as we meet with it in many 
amphibians, has not either that character at so early an age 
in Dipnoi and Ganoids ; the homologue of it is found in the 
Schwanzknopf, as we also saw in Elasmobranchs. And 
Fig. 87, for Amia, indicates, moreover, if we compare it 
with Fig. 99 for Tarsius, that the intestinal continuation al 
in both figures is of the same order, although in the mammal 
it is no slit, but has become a tube. Moreover, both of them 
may be brought into line with Kupffer’s vesicle in Teleosts. 
In many respects the development of the Teleosts offers 
peculiarities not met with in the Vertebrates hitherto dis- 
cussed. ‘The process of notogenesis has certain remarkable 
points of comparison with what we notice im many Amphibia. 
Ziegler has, in his ‘Lehrbuch der vergl. Anatomie der 
niederen Wirbeltiere’ given four coloured diagrams (Figs. 
11—14) to accentuate the extent of this comparability, and 
says in his text (p. 182): ‘The ventral border of the blasto- 
derm advances quite in the same way as does the ventral 
point of transition between the smaller and the larger cells 
in Rana and Triton.” 
However, there are numerous points of divergence and the 
different authors who have of late occupied themselves with 
