424 Prof, G. Retzius. Principles of the [June 15, 
Fic. 6.—Head of small Crustacean (Daphnia, male), from the right side, showing several 
nerve elements coloured (black). On the left is the brain ganglion, with nerve-cells, 
and on the right side of it the smaller optic ganglion, in which the optic nerve-fibres, 
coming from the eye, end. Below, there is seen in the figure the bipolar sensory cells 
in the first antenna, constituting the so-called organ of smell, with central fibres 
going to the basis of the brain-ganglion. In the second antenna two tactile cells, with 
leng central fibres are seen. 
independent of one another, and do not enter into connection one with another. 
In agreement with the statement of v. Kupffer, in 1857, His observed the 
nerve-fibres of the embryo growing as axis-cylinder-processes of the nerve- 
cells; v. Kupffer and His considered, moreover, every nerve-fibre in the body, 
both in the nervous central organ and in the peripheral parts of the body, to 
be processes of that kind more or less lengthened. 
a ‘. 
