252 CLAYPOLE: [VoL. XIV. 
from the holoblastic egg. The cells have arranged themselves 
in two definite layers which differ slightly in character. The 
outer layer is continuous, while the inner is composed of fewer 
cells at regular and greater distances apart. Some cells remain 
behind in the yolk. Following this there is a rapid division of 
the cells forming these two layers, until a stage shown in Fig. 
35 is reached. Cell outlines become very indistinct in the 
blastoderm and the size very much reduced. The protoplasm 
becomes strongly vesicular. Some of the cells left behind in 
the yolk cease division at a much earlier stage and remain 
large, lying in the yolk; others are grouped in masses (Fig. 
BONE LIE 
These are the principal steps in the cleavage and formation 
of the blastoderm as found in Anurida, and they can be seen 
to widely diverge from the centrolecithal cleavage and conse- 
quent migration of the cells typically found among insects. 
Unequal holoblastic cleavage has been described by Lemoine 
(87) in Smynthurus and retarded holoblastic in Anurophorus. 
Ryder ('86) while describing some of the later embryological 
features of Anurida does not consider the early stages, so 
makes no note of the cleavage. Smynthurus and Anurophorus 
were not studied in section, so that internal changes were not 
described. In Anurida, as has been seen, there is a sudden 
change in the method of development, which results in the final 
formation of the blastoderm by migration, as in the case of the 
typical centrolecithal egg. The temporary preservation of the 
yolk blastomeres suggests the condition found in a centroleci- 
thal egg after the blastoderm is formed and secondary yolk 
cleavage has occurred. 
Before discussing possible interpretations of the facts ob- 
served in Anurida, a brief sketch of some other somewhat 
peculiar methods of cleavage will be attempted. There is no 
other arthropod as yet described in which cleavage takes place 
in just this way. Many are holoblastic at first and change 
their method of cleavage during development. Among the 
crustaceans are found some interesting forms. Korschelt and 
Heider ('92) classify crustaceans according to cleavage methods, 
and put in the second group all those forms which start with 
