The Development of the Olfactory Organ in the Teleostei. 621 
with Alum-Carmine or Erticn Haematoxylin. They were then em- 
bedded in paraffin and complete series of the head cut by microtome. 
In later stages, where the cartilage had commenced to develop, 
double staining was used, with Erosin for Haematoxylin, and Aniline 
Blue for Carmine, preparations. 
The first indication of the development of the organ in embryos 
of 28 to 30 days, is given by the appearance of two thickened spots 
in the ectoderm, situated symmetrically to the middle line of the 
embryo, in very similar position to those of Elasmobranch fishes as 
described by BALFour in his work cited in my introduction, that is, 
laterally, on the ventral part of the head, a little forward of the 
eye. They consist of a few layers of cells, which have generally 
a somewhat radial appearance and are not unlike the sense or taste 
organs in the integument of fully developed fishes. Fig. 1, Plate XVII, 
shows transverse sections from embryos of 28 days; Fig. 2, shows 
similar sections from embryos ten days older. The organ is by this 
time laying close on the neural canal, only separated by a membrane 
which seems to be formed by the basal cells of the organ. The 
first sign of any mesoderm is seen in Fig. 1, m, but it develops 
quickly and the next stage is shown in Fig. 2. In the early stages 
now described I have not found any differentiation of the tissue 
into olfactory cells or elongated columnar epithelial cells, but in the 
following stage (Fig. 3, Plate XVII, which shows a sagittal section 
of an embryo 46 days old) some elongated cells can be perceived 
amongst the ordinary embryonic tissue. At this time the organ has 
an elongated appearance, still on the ventral side of the head; the 
olfactory lobe (ol.o. Fig. 3) is descending towards the foremost 
situated part of the organ and is connected with this through rows 
or aglomorations of cells similar to those of which the lobe itself 
consists. The external outline of the organ is in this stage perfectly 
on the same level as the outline of the embryo and no involution 
has commenced. Any olfactory nerve proper cannot be discovered 
in this stage and probably it is not formed out of the cells connee- 
ting the olfactory lobe with the organ. HorrmMann gives some in- 
formation about the development of the olfactory nerve, but the age 
and development of his embryos are given in an uncertain manner 
and almost without figures, so that I do not venture to draw any 
conclusion there-from or make comparisons with my results. 
The development is at this stage very slow and no distinct 
change can be seen until the embryo has attained 60 days. 
