ce 
“ 
44. 
45. 
48. 
49, 
MUSEUM OF COMPARATIVE ZOOLOGY. 101 
. 43, 46, 47. Blastodermic cells ; to show some of the conditions presented by 
the chromatine and nucleoplasm of their nuclei. 
A cell in the process of division, further advanced than the one repre- 
sented in Fig. 42. 
A portion of Fig. 49 highly magnified to show the columnar nature of the 
ectodermic cells and the complete differentiation of the mesoderm. 
Ectodermic cells with two nuclei from a late stage, during the infolding, 
to form the ovary. 
Sagittal section through an embryo in the protozonite stage, X 110. 
Note. — In cutting and mounting, the section was artificially ruptured in 
two places, but none of the blastoderm has fallen away. 
PLATE VIII 
Sagittal section through an embryo during reversion, showing stomo- 
deum, tail-lobe, etc. XX 110. 
51, 52. Views of sagittal sections of the posterior region during reversion, to 
55. 
5€. 
g. 57. 
58. 
60. 
61. 
62. 
show the condition of the tail-fold. 
Section of the tail region and a part of the dorsal region, to show the 
mesodermic somites of the rudimentary terga. The section is cut 
obliquely to the median plane. X 110. 
Sagittal section of the morphological tip (7) of the body near the close 
of reversion, to show the early condition of the proctodeum. x 110. 
Sagittal section of the hind part of the body, to show the stercoral pocket 
(br. ste.) and the pre-stercoral tube (pr-stc.). 
Sagittal section of the hind part of the body, to show the trumpet-shaped 
condition of the pre-stercoral tube and the somatization of the body as 
indicated by the segmental grouping of the muscles (mu. 1— mu. 5). 
PLATE IX. 
A nearly horizontal section of the proctodeum and the stercoral pocket 
(br. stc.), about three days before hatching, showing the columnar 
epithelium and the narrow lumen of the proctodeum. X 310. 
Sagittal sections of anus and stercoral pocket, about eight days after 
hatching. X 110. 
About one half of a transverse section in the region of the “ rudimentary 
terga,” to show the mesodermic somites of these dorsal elements and 
their connection with the ventral portion of the mesoderm. > 100. 
Transverse section of an embryo near the beginning of reversion, pass- 
ing through the stomodzum and the 2nd pairs of legs. 100. Com- 
pare the separated nerve bands (gn.) with those of Fig. 62. 
A section from the same embryo as Fig. 59, showing entodermic cells 
(en.) in the region of the tergal elements. 
Transverse section after completed reversion, through that part of the 
stomodzum which becomes the sucking stomach. Itshows the mus- 
cles attached to sucking stomach (mu. vrt., mu. lat.), and the approxi- 
mation of the nervous bands (gn.). > 110. 
