76 ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 
to the cephalic pole of the embryo; and this view has been supported by 
Garbowski (1898); on the other hand, Kowalevsky (1867) and many recent 
writers on the development of Amphioxus (Lwoff 1894, Klaatsch 1896, Samassa 
1898, Morgan and Hazen 1900), have considered that the most highly arched 
portion of the late gastrula represents the animal pole. Since this point is said 
to become the anterior end of the embryo it is evident that according to this 
view the chief axis of the egg coincides with the chief axis of the embryo and 
is antero-posterior in direction, whereas in ascidians it has heretofore been claimed 
that the egg axis is dorso-ventral in direction and hence perpendicular to the 
same axis in Amphiorus. 
Such diversity in this most fundamental of all axial relations seems very 
improbable considering the many points of resemblance between these groups, 
and atleast such conflicting results should be supported by the best of evidence 
before being given general uide 
Korschelt and Heider in their excellent text bodie attempt to harmonize these 
differences in axial relations between Amphzoxus and the ascidians by regarding 
the anterior pole of the ascidian gastrula as the animal pole, but I agree with 
Samassa (1894), and Castle (1896), that the animal pole never comes to lie at the 
anterior end of the embryo, though unlike them I hold that it does move in that 
direction. 
In Amphioxus as in the ascidians the anterior limit of the neural plate is 
situated some distance behind the most highly arched portion of the gastrula, 
and even if the latter be regarded as the animal pole it would still be true of 
Amphioxus as of the ascidians that the neural plate does not reach as far forward 
as the animal pole. But there are reasons for thinking that the animal pole lies 
ventral to the most highly arched portion of the Amphzoxus gastrula. Many inves- 
tigators agree that the animal pole lies opposite the blastopore ; Samassa has observed 
in a small percentage of eggs that the polar body is still attached to the embryo at 
a time when the-blastopore is growing smaller, and in all such cases he found it at 
the pole opposite the blastopore (although, as he maintains, at the anterior end of 
the embryo). But the point opposite the blastopore lies ventral to the most highly 
arched portion of the embryo. Even if it should be assumed that both ventral and 
dorsal lips grow equally, the animal pole would still be located on the ventral side 
of the most highly arched portion, owing to the peculiar shape of the embryo; if 
the dorsal lip grows more rapidly than the ventral, which in the light of what 
takes place in ascidians and amphibians seems probable, the animal pole must lie 
still farther toward the ventral side. In any event a considerable space must inter- 
vene between the anterior limit of the neural plate and the animal pole. 
The work of Garbowski (1898), shows that the longitudinal axis of the larva 
of Amphioxus forms an angle of about 70° with the gastrular axis,—a result which, 
like that of Hatschek and Sobotta, agrees very closely with my observations on 
ascidians, and which practically removes the supposed discrepencies in axial rela- 
tions between these two classes. 
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