Bovzr. — Mesoderm in Teleosts. 
PUATE"YV, 
Material treated the same as in the case of Plate IV. Figs. 80-34 from an embryo 
of 84 hours. Figs. 85-37 from an embryo of 108 hours. 
Fig. £ 
3: 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. : 
Vig. 
36. 
Figs. 30-37. Transverse Sections. (Magnified 310 diam.) 
Through the second protovertebra, being in front of the evagination 
forming the nephrostome, and showing that the somatopleure is com- 
posed of a single layer of cells. 
Through the third protovertebra, showing the anterior region of the 
nephrostome. 
The next section back of the one from which Fig. 31 was taken. 
Through the posterior region of the third protovertebra. 
Through the posterior region of the fifth protovertebra. The lateral por- 
tion of the intermediate cell-mass has formed the segmental duct 
(dt. sg.), and has separated from the axial portion of the intermediate 
cell-mass (cl.-mo. i'm). The aorta is not yet formed, and the intes- 
tine (in.) is not closed. 
Section of an embryo 24 hours older than that of Fig. 34, representing 
the same region. In this embryo the aorta (ao.) is formed as far 
forward as the third protovertebra. There remain in this region a 
relatively small number of undifferentiated nuclei of the intermediate 
cell-mass. The segmental duct (dt. sy.) is completely formed. 
From the eighth protovertebra of the same embryo as Fig. 35. The 
aorta is not yet formed. The axial portion of the intermediate cell- 
mass is relatively large. The segmental duct (dt. sg.) is formed, and 
the intestine (in.) has closed in and assumes a tubular form. 
From the posterior trunk region of the same embryo, showing a volumi- 
nous intermediate cell-mass (el.-mo. Um). The segmental duct (dt. sy.) 
is not distinctly separated from the axial cell-mass, and shows as yet 
no trace of alumen. The intestine has not yet assumed its tubular 
form. 
