iE | 
CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 
E MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 
COLLEGE. E. L. MARK, Drrecror. No. 182. 
in 
0. 
. Sixthcleavage. Sixty- 
two cells. Closing 
of the  blastopore. 
The germ-layers 
Seventh cleavage. 
The mesoblast 
‘(L. — NO. 2 
XII. General 
A Study of Cell-Lineage 
11. Review of literature 
on late stagesof cleav- 
age, on closing of 
blastopore and on 
differentiation of the 
germ-layers : 
of 
a. Late stages 
cleavage . 
b. Closing of blasto- 
pore 
c. Differentiation of 
the germ-layers 
12. Determinate cleavage 
3. Notes on cleavage and 
germ-layers in L. 
fascicularis 
Extension of the mesoblast 
and entoblast. Later de- 
velopment of the germ- 
layers 
Formation of the. append- 
ages of the Nauplius, and 
development of the or- 
gans 
General considerations” on 
cleavage and cell-lineage. 
Comparison of the germ- 
layers of Lepas with those 
of other Crustacea . 
summary, with 
table of cell-lineage of 
Lepas 
trarly Development of Lepas. 
and Germ-Layers. 
By Maurice A. BIGELOW. 
} 
TABLE OF CONTENTS. 
PAGE 
roduction 62 
itorical F : 63 
terials and methods . 64 
turation and fertilization. 
che unsegmented ovum. 68 
Review of literature on 
maturation and fertil- 
ization ‘ 71 
aeral sketch of cleavage 
nd germ-layers 73 
menclature of cleavage. 74 
savage . ; 77 
1. Introductory . cr ae 
2. First cleavage. ‘Two 
cells . 77 
3. Review of the litera. 
ture on first cleavage 85) VIII. 
t. Second cleavage. Four 
cells . 89 
5. Review of the litera 
ture on the second IX. 
and succeeding cleay- 
ages . . 91 
6. Third cleavage. Fight 
| cells . ; 98 te 
(7. Fourth cleavage. Six: 
teen cells . . £10 SE 
(8. Fifth cleavage. Thirty- 
‘ two cells . 102 
104); Addendum . 
Bibliography : : 
111| Explanation of Plates : 
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