Boyer. — Mesoderm in Teleosts. 
PLATE IV. 
The material from which the drawings of this plate are made was killed with 
Perenyi’s fluid, stained with Kleinenberg’s haematoxylin; sections are 74m in 
thickness and magnified 810 diameters. Figs. 23 and 24 are from an embryo of 
about 5 days, and all the others from an embryo of 3} days. 
Fig. 23. 
Fig. 25. 
Fig. 26. 
Fig. 27. 
Fig. 274. 
Fig. 28. 
Fig. 29. 
Figs. 23-29. TRANSVERSE SECTIONS. 
Through the region of the auditory vesicle and third gill-cleft, showing 
the small volume of mesoderm and relatively large space occupied by 
the endodermal evagination forming the gill-cleft (/s. brn.). The sec- 
tions give an anterior view on the left side. 
Through the region of the fourth gill-cleft, showing an earlier stage of 
endodermal evagination than Fig. 23, and a relatively large amount 
of mesoderm still in its original position. 
Through the region of the second protovertebra, showing the ventral 
shifting of the lateral layers, and nuclei (/.*) of protovertebral origin 
and some (n/.+) of doubtful origin. 
Through the posterior region of the third protovertebra, being the region 
in which the nephrostome is formed later, showing also the shifting 
of the lateral plates along the protovertebrx and the migration of cells 
from the lateral plates toward the median line. 
Through the middle region of the third protovertebra, showing three nu- 
clei (n/.*) under the chorda, which probably have a protovertebral 
origin. ; 
Through the posterior region of the third protovertebra, showing the 
migration of nuclei from the lateral plates toward the median line. 
Through the middle region of the fifth protovertebra, showing the “inter- 
mediate cell-mass” cut off from the lateral layers, and nuclei passing 
from its proximal margin toward the median line. 
Through the posterior region of the fifth protovertebra, showing nuclei 
from the “intermediate cell-mass” in position under the chorda. 
This section represents a condition in which only a few cells have 
taken their place between the chorda and entoderm ; but in the fourth 
section back of this, the mass of cells in this position is three to four 
cells in thickness. 
