320 LANGENBECK. [VoL. XIV. 
described above, which were absorbed. In eggs at about the 
stage represented in Fig. 33 I have seen cells in the anterior 
part of the head region which were apparently migrating off into 
the yolk area, as the one shown in Fig. 49, but these lay very 
near the surface, and in the stages shortly before the entodermal 
invagination had appeared cells were never seen in the yolk 
area. I conclude, therefore, that these were probably dorsal 
cells which were overgrown, and had not taken their final posi- 
tion at the time when the egg was killed. Cells which appear to 
be similar to these were described by Dr. Pereyaslawzewa ('88), 
who considers them to be entoderm cells derived from the 
ventral plate and migrating into the yolk area. Ido not be- 
lieve, however, that in Microdeutopus they take any part in 
the formation of the entoderm. 
Ulianin (81) finds a number of cells scattered through the 
yolk area which he supposes are derived from the dorsal organ, 
as at first they are found in that region. He leaves the 
origin of these cells an open question, however, as he was not 
able to secure a complete series of embryos, and, therefore, 
could not trace them to their source. The whole entoderm, 
according to Ulianin, is derived from these cells, and the lower 
layer cells of the ventral plate form mesoderm only. Dr. Pereyas- 
lawzewa ('88) believes that the entoderm is derived from two 
sources, from the ventral plate and from the dorsal invagina- 
tion, which she considers to be the dorsal organ, as the follow- 
ing passage states: “ A mesure que l’organe dorsal se développe, 
l’ectoderme avoisinant s’épaissit visiblement et garde pour 
longtemps cette configuration, vu qu'il ne détache aucun 
organe nouveau. Ce rdle passif qui lui est propre, me permet 
de le comparer a la plaque dorsal chez les Insectes. La dis- 
semblance consiste en ce que chez ces derniers la formation 
de la plaque précéde celle du tube, tandisque chez les Crusta- 
cés nous remarquons le contraire. D’aprés les recherches de 
M. Korotneff sur le développement de Gryllotalpa les cellules 
qui dérivent en grande nombre de la plaque dorsal s’introdui- 
sent dans les masses nutritives et apres les avoir élaboré de 
maniére a les préparer pour l’assimilation, qui aura lieu dans 
les cellules de l’intestine, elles se détruisent completement. 
