78 
IOWA ACADEMY OF SCIENCES. 
auditory stimulation. But the most significant fact, it 
seems to me, is that the pars basilaris is either absent or 
very imperfectly developed. This structure which finally 
evolves into the cochlea of the higher Vertebrates, is dis- 
tinctively the organ of hearing, according to recent physi- 
ological interpretation. 
We then, in all probability see in this transition class of 
Vertebrates, the Amphibia, the origin of an organ of hear- 
ing from an organ of equilibration, which latter function 
is always retained. To be sure it may be suggested that the 
lack of a pars basilaris in Proteus, Nectums, etc., may be 
due to degeneration. Admitting this possibility, yet as I 
have elsewhere shown, in the development of the ear of the 
Salamander, Ambly stoma, the pars basilaris is the last of 
the parts of the labyrinth to be differentiated, and then 
only near the close of the larval period. That is, the order 
in which this structure appears in the embryo, undoubt- 
edly corresponds to the way in which it originated in 
the Amphibians as they were evolving from the ancestral 
aquatic condition into the semi-terrestrial state of existing 
species. 
A COMBINATION OF CHROMIC ACID, ACETIC ACID 
AND FORMALIN AS A FIXATIVE FOR 
ANIMAL TISSUES. 
H. W. NORRIS. 
That many of the fixing reagents in common use in the 
preparation of tissues for histological study are poorly 
adapted to the fixation of the ova and embryos of Amphib- 
ians, is evident to any one who gives more than casual 
attention to the matter. The large amount of yolk pres- 
ent in the cells of the Amphibian embryo makes completely 
uniform fixation with some reagents impossible, and then, 
too, the disintegrating effect of many fixing fluids upon 
the yoke granules makes the result very unsatisfactory. 
A fluid that gives good fixation is likely to interfere with 
