1891. | Recent Studies of the Vertebrate Head. 335 
Beard (’89@) reiterates his former conclusions that the nose, like 
the ear, represents a branchial sense organ. The olfactory nerve, 
like a typical branchial nerve, develops from two sources: from 
the ectoderm just outside the foundation of the central nervous sys- 
tem, and from the special neuro-epithelium The latter grows in 
length by increase within itself, and later on in development, in 
many cases it divides up into a number of smell-buds, comparable 
exactly to the sense organs of the lateral line. The origin of the 
olfactory nerve in reptiles ıs essentially similar to that in Elasmo- 
branchs. In the chain connecting the sensory cells of a verte- 
brate sense organ with the central nervous system there are gan- 
glion cells arising from three different sources: from the neuro- 
epithelium itself; between the lateral ganglion and the central 
nervous system ; as a special differentiation in the central nervous 
system. Jacobson’s organ is a specially differentiated part of the 
nose. , There is nothing in the development of the nose per se to 
suggest a gill-cleft. 
Golowine (’90a) confirms many of the statements of Beard. 
He thinks that in the chick the ectoderm situated at the sides of 
the not-yet-closed medullary tube represents two sensitive organs, 
and that from these latter the ganglionic system is developed. 
Beard had stated that the ganglion Anlagen are, after the first 
Stages, independent of the ectoderm, but Golowine observed their 
formation from ectoderm cells up to the time the neural ridge is 
complete. In most respects he agrees with Beard as to the 
origin of the Anlagen. Before the neural ridge segments it be- 
comes separated from the sensitive ectoderm by a layer of indif- 
ferent ectoderm. Thus in the so-called sensitive organ can be 
recognized two distinct portions: ganglion Anlagen and the 
Anlagen of the special sense organs. The neural ridge in the 
cephalic region divides successively into three ganglion groups. 
Kastschenko’s conclusion that the dorsal parietes of the medul- 
lary tube deggnerates to such an extent that a second closing 
Occurs is erroneous. As the neural ridge divides, to each gan- 
glionic se t isa tof sensitive ectoderm, which 
has E > 
* Beard, it should be remembered, holds that th iral ridge is independent of th 
tral nervous system : 
Am. Nat.—April.—3. 
