140 
cap‚ while the bilateral polarity is only slightly manifested, the 
cells of the rear side not being much larger than those 
of the anterior side. On the other hand, this last condition 
prevails very strongly in Scoloplos which accordingly can 
serve as an eXample of the predominance of the bilateral pola- 
rity. The cell 2d especially is of extraordinary size, 
while the endoderm cells are not at all remarkable for 
a. b. zl 
Fig. 38. Diagrammatic representation of the 3 types of the eggs of 
polychaetous Annelids. 
[, U, III, Ist, 2nd, and 3rd quartet of ectomeres. 
ent. entomeres. 
a. minute egg, b. egg with pronounced radial polarity, c. €88 
with pronounced bilateral polarity. 
The animal pole is indicated by a black dot. 
special bulk. Thus the endoderm area, as s the 
diagram c of fig. 38, is displaced here to the ventral side 
from the beginning, as is found in the same way in the 
egg of the frog where, however, the cleavage process 1S 
much more independent of the constitution of the egg. 
In this way, 1 believe, is the dorsad displacement of the 
endoderm area in the egg of lower Vertebrates to be 
explained '). 
1) Thus the Amphibian egg in its structure corresponds to the 
Scoloplos-type among Annelids. In a former article (1916 b) 1 was 
le mpare the egg of Rana esculenta to the type of Nereis. 
that there is no such great difference between the eggs of Rana fusca 
abnormally developing eggs of the latter species. 
