236 BEATRICE WHITESIDE 
more into 100 per cent alcohol (two hours) and then into xylol 
(one hour). ‘They were then placed in a bath of xylol-paraffin 
(two hours), in paraffin 40° (eighteen hours), and finally in 
paraffin 58° (six hours). The best stains were obtained by a 
combination of haemalum with picrie acid. Many larvae were 
also prepared macrosopically. 
Stage I (fig. 2) 
The youngest larva that I examined was 4 mm. long (measured 
from the tip of the head to the aperture of the anus). The mouth- 
opening and internal gills had appeared. 
The invagination and constricting off of the auditory sac had 
also'taken place. The latter organ has now a somewhat spheri- 
cal form, and, as in this stage there is no cartilaginous capsule, 
it lies close to the side of the hind-brain, being separated from 
this by a thin layer of mesoderm cells (fig. 2). On its medioven- - 
tral side the ganglion acusticus (g.a.) lies between it and the 
brain. It is divided into utriculus (wir.) and sacculus (sac.) 
by a septum and already possesses the rudiments of the semicir- 
cular canals, lagena, pars neglecta, and pars basilaris. Within 
the auditory sac numerous lime otoliths can be seen. 
The ductus endolymphaticus (d.e.) is a well-differentiated 
canal, situated at the median side of the auditory sac. This 
duct starts from the upper median part of the sacculus and runs 
dorsally at the median side of the-utriculus, extending in a dorsal 
direction even further than the latter organ. Its long axis thus 
runs in a dorsoventral direction. In contrast to later stages, 
it is large in comparison with the auditory sac. 
At its upper end the ductus expands into a small vesicle, 
whose diameter is about twice as large as that of the ductus 
proper. This vesicle extends somewhat in a cranial direction. 
It represents the rudiment of the saccus endolymphaticus (s.e.). 
The histological structure of the ductus and saccus endolym- 
phaticus at this stage, in contrast to later ones, is exactly alike. 
This corresponds to the fact, established by Alexander (’90) and 
confirmed by Fleissig (’08), that in the development of the laby- 
rinth the histological differentiation sets in much later than the 
