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ME. F. M. BALFOTJE ON THE DEVELOPMENT OF 
PLATE 17. 
'Fig. E a. Section of a Pristiurus-embryo belonging to the second stage. Camera. (Zeiss 
CC ocul. 2.) The section shows the constriction of the pedicle which attaches 
the posterior nerve-rudiments to the spinal cord. 
pr, rudiment of posterior nerve-root ; nc , neural canal ; mp, muscle-plate ; 
vr, vertebral rudiment; sd, segmental duct ; cli , notochord; so, somatopleure ; 
sp, splanchnopleure ; ao, aorta ; al, alimentary canal. 
Fig. Eb. Section of a Pristiurus-embryo slightly older than Ea. Camera. (Zeiss CC 
ocul. 2.) The section shows the formation of the anterior nerve-root ( ar ). 
ar, rudiment of the anterior nerve-root. 
Fig. F. Section of a Pristiurus-embryo with the rudiments of five visceral clefts. Camera. 
(Zeiss CC ocul. 2.) 
The rudiment of the posterior root is seen surrounded by connective-tissue, 
from which it cannot easily be distinguished. The artist has not been very 
successful in rendering this figure. 
Figs. G 1, G 2, G 3. The longitudinal and horizontal section of an embryo somewhat 
older than F. The embryo from which these sections were taken was hard- 
ened in osmic acid, but the sections have been represented without tinting. 
G 1 is most dorsal of the three sections. Camera. (Zeiss CC ocul. 1.) 
nc, neural canal ; sp.c, spinal cord ; pr, rudiment of posterior root ; ar, 
rudiment of anterior root; mp, muscle-plate; c, connective-tissue cells; 
ch, notochord. 
Fig. H i. Section through the dorsal region of a Pristiurus-emhryo in which the rudi- 
mentary external gills are present as very small knobs. Camera. (Zeiss CC 
ocul. 2.) 
The section shows the commencing differentiation of the posterior nerve- 
rudiment into root {pr), ganglion ( sp.g ), and nerve ( n ), and also the attach- 
ment of the nerve^root to the spinal cord ( x ). The variations in the size and 
shape of the cells in the different parts of the nerve-rudiment are completely 
lost in the figure. 
pr, posterior nerve-root ; sp.g, ganglion of posterior root ; n, nerve of poste- 
rior root ; x, attachment of posterior root to spinal cord ; w, white matter 
of spinal cord ; i, mesoblastic investment to the spinal cord. 
Fig. H II. Section through the same embryo as H i. (Zeiss CC ocul. 1.) 
The section contains an anterior root, which takes its origin at a point 
opposite the interval between two posterior roots. 
The white matter has not been very satisfactorily represented by the artist. 
Figs. 1 1, I ii. Two sections of a Pristiurus-embryo somewhat older than H. Camera. 
(Zeiss CC ocul. 1.) 
The connective-tissue cells are omitted. 
Figs. Ia, I b, I c. Three isolated cells from the ganglion of one of the posterior roots of 
the same embryo. 
