DEVELOPMENT OF THE SACCUS ENDOLYMPHATICUS Zyl 
tubul. These again split up into still smaller ones. In the 
main part of the saccus all the tubuli run in a ecraniocaudal 
direction. ‘The processus ventralis consists of four or five com- 
paratively large tubuli running in a dorsoventral direction and 
coalescing in several places (fig. 8). The partes spinales and the 
12 
Figs. 11 to 19 Diagrams of the central nervous system and labyrinth (Sac- 
cus endolymphaticus black). Spinal ganglia not drawn in figs. 11 to 14. 
Fig. 11 Dorsal view of larva. (Stage II.) d.e., ductus endolymphaticus; 
l, labyrinth; sac., sacculus; s.e., saccus endolymphaticus; wtr., utriculus; ven. 4, 
fourth ventricle. 
Fig. 12 Dorsal view of larva (Stage III.) Jl.opt., lobi optici. 
calcareous sacs are composed of a large number of tubuli. In 
each pars spinalis there are three of these structures. Figure 9 
represents a transverse section in the region of an interverte- 
bral foramen. I found that the tubuli of one-half of the partes 
spinales never join with those of the other half. The connec- 
tion between the partes posteriores of the two sacci endolym- 
