Houser, The Neurones of a Selachian. 71 
designated Jobe optique, and the anterior end of the oblongata 
the cervelet.* 
2. Work on the Microscopical Anatomy of the Brain. 
Anatomical work on the nervous system of the Selachii 
was begun relatively early, but microscopical study lagged 
somewhat behind that on the bony fishes. One of the earliest 
researches touching the microscopical structure of the selachian 
brain was that of Lrypiec (’§2). This versatile investigator was 
engaged in tracing the general organogeny and histology of the 
rays and sharks, and so his work upon the brain was not special 
in its character. Here, however, he discovered the olfactory 
glomeruli, a result altogether sufficient in itself. Of course, the 
nature of the microscopical methods then in use did not permit 
Lerypic to see much more than the general outline of a glom- 
erulus and the fibres associated therewith. It remained for later 
workers to trace the full significance of his discovery. 
The two decades following the research of Lrypic wit- 
nessed the unfolding of the germ of a special neurological tech- 
nique. SrTiLLinG had introduced the method of studying the 
brain by means of sections as early as 1842, but the great ad- 
vantages to be derived from staining the sections were not 
realized until 1858, when GERLACH soaked his sections ina 
solution of carmine. Later, 1872, GERLACH obtained such 
brilliant results with gold chloride as to lead to many trials with 
this reagent, while some of the possibilities of osmic acid were 
also becoming known. Finally, chromic acid and the bichro- 
mates had come to be recognized as valuable means for harden- 
ing nervous tissues. Fortunate that man who was permitted to 
contribute to the inauguration of a new era in the comparative 
study of the nervous system, the era of microscopical research. 
Two investigators extended such a possibility to the field of the 
selachian brain at practically the same time, ViAULT publishing 
his results in 1876, and Rouwon in 1877. ; 
The research of ViauLr (76) is quite broad in its scope. 
1 Route, L.: L’Anatomie Compareé des Animaux, Tome 2, Fig. 1137. 
Paris, 1898. 
