Boyer. — Mesoderm in Teleosts. 
PLATE VI. 
All drawings on this plate are from embryos at 96 hours. Figs. 39-44 inclusive 
are from the same embryo; it was killed with Perenyi’s fluid and stained with 
Kleinenberg’s hematoxylin. Sections 74 thick. 
Fig. 88. Dorsal view of a portion of a clove-oil preparation to show the relative 
position of the pectoral plate and the anterior protovertebre. The 
principal part of the somatopleuric thickening which constitutes the 
pectoral plate is opposite the first four protovertebre (1-4). 65. 
Figs. 89-44. Transverse Sections. (Magnified 310 diameters.) 
Fig. 39. In the region immediately in front of the first protovertebra. The axial 
mesoderm extends laterally continuous with the somatopleure (so’p/u.). 
lig. 40. From the first protovertebra. Here the protovertebra (pr’vr.) passes 
gradually over into the pectoral plate (/a. pet.). The peripheral cells 
define the contour of the protovertebra only in its upper region. In 
the region of the pectoral plate no boundary of the protovertebra is 
distinguished. The space between ectoderm and mesoderm is due to 
their artificial separation during preparation. 
Fig. 41. From the second protovertebra, showing the same histological connection 
between the protovertebra (pr’vr.) and pectoral plates (/a. pet.) as is 
shown in Fig. 40. This section is taken from the posterior region of 
the (second) protovertebra, and is the tenth section (75) back of the 
one represented in Fig. 40. The intervening sections represent the 
same relation between protovertebra and pectoral plate. 
Fig. 42. From the third protovertebra, showing less advancement in the develop- 
ment of the pectoral plate than in the preceding sections, and not so 
firm a connection between it (/a. pet.) and the protovertebra (pr. vr.). 
The section passes through the middle of the nephrostome ( pr’nph.). 
Fig. 43. From the fourth protovertebra, showing the pectoral plate as a single 
layer of cells and continuous with the somatopleure (so’plu.). No 
definite connection between somatopleure and protovertebra is shown. 
The section passes through the segmental tube (70. sg.). 
Fig. 44. From the sixth protovertebra. The somatopleure (so’plu.) shows no trace 
of any thickening to form the pectoral plate, and it has apparently no 
connection with the protovertebra. 
