28 ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 
(4) In the 16-cell stage the 8 dorsal endodermal cells are yellow and have 
small nuclei; the 8 ventral ectodermal ones are clear (p. 50). 
In the identification of individual cells and their axial relations Seeliger was 
much at fault. The small cells of the 4-cell and later stages are certainly not ante- 
rior in position but posterior, as has been shown by Van Beneden and Julin, Cha- 
bry, Samassa, and Castle; while the two larger cells of the 8-cell stage are not ven- 
tral but dorsal in position, not posterior but anterior, as their relations to the two 
small posterior cells show. Seeliger therefore mistook anterior for posterior, dorsal 
for ventral and consequently right for left; in short, he committed all the mistakes 
possible in orientation. 
9. Samassa’s System. 
Ten years after the publication of Van Beneden and Julin’s work, Samassa 
(1894) working on Crona and Clavellina reached very different conclusions from 
those set forth by the first named authors. With the first four conclusions of Van 
Beneden and Julin mentioned above he agrees, save that in the unsegmented ере 
he claims that only the median plane and the anterior and posterior, but not the 
dorsal and ventral, poles can be recognized. With regard to the identification of 
the dorsal and ventral sides he held that Van Beneden and Julin were completely 
in error and that they had mistaken the dorsal for the ventral, the endodermal for 
the ectodermal pole in: all stages up to the 44-cell stage. As the most important 
evidence of this false orientation Samassa cites Van Beneden and Julin’s figures 9 ¢ 
and 10 с, which represent optical sections in the sagittal plane of а 32-cell and a 
44-cell stage respectively. In the first of these the ectoderm’ cells are shown as 
columnar, the endoderm cells as flattened; whereas in the second, figure 10 c, the 
ectoderm cells are flattened and the endoderm columnar. “The figures of these 
two authors," says Samassa, “are sufficient to show that figure 10 с is properly and 
figure 9 с falsely oriented; in both cases the cylindrical cells belong to the endoderm 
and are dorsal in position.” The words of Samassa directed against Van Beneden 
and Julin apply with equal or even greater force to himself: “ Van Beneden and 
Julin have not once sought,” he says, “to bring forward one fact in support of this 
remarkable transformation.” With the exception of the worthless а 272072 argu- 
ment that cells which have once been cylindrical must always remain so Samassa 
has not produced a single argument or fact in favor of his contention. 
4. Castles System. 
In the same year Castle (1894), in a preliminary paper and again in his 
final paper (1896) on the early embryology of Crona zntestzna/zs, reversed the orien- 
tation maintained by Van Beneden and Julin and held with Samassa that in all 
stages preceding the 44-cell stage the Belgian investigators had mistaken dorsal 
for ventral and vzce versa. Furthermore, after having studied the formation of 
the polar bodies, he was lead to the truly remarkable conclusion that these bodies 
in ascidians are formed at the endodermal pole, whereas in all other animals, so 
