186 General Notes. [February, 
as the author suggests, many new forms remain to be detected. 
Notes on collecting and preserving these forms, and a few de- 
scriptions of marine copepods from the Gulf of Mexico are 
added. The figures are numerous and fairly well drawn, some 
being anatomical and embryological in their nature. 
The work will do credit to the author and be of service in 
directing attention to these creatures, and it is to be hoped that 
the author will be able to add to and extend the work, and ina 
few years give us an enlarged and improved edition of it,as a 
hand-book of our fresh-water Entomostraca would be useful. 
The plates should have been numbered not lettered ; Limnetis 
is spelt Limnetes, but the typographical errors are not numerous, 
MORPHOLOGY OF THE VERTEBRATE AUDITORY OrGAN.—The 
chief vertebrate sense organs have certainly had a very 
different origin. The olfactory organ is probably a modified gill 
olfactory and auditory nerves as well as the eye. But recent 
researches, especially those of Marshall and Van Wijhe, have 
proved that the auditory nerve is merely a dorsal sensory branch 
of the 7th cranial nerve (3d segmental nerve of Van Wijhe). 
It has been shown above that the nerves which supply the 
segmental sense organs are dorsal sensory branches of the seg- 
mental nerves, that the segmental sense organs are merely modi- 
fied portions of the epiblast, that these sense organs primitively, 
and in some existing form still throughout life, lie free on the 
surface of the body, but that later in most cases they become 
shut off from the epidermis in a sac which remains connected 
with the external world by a small opening. The sensory cells 
of these organs possess long fine terminal hairs, which are easily 
affected by wave-motions in the medium in which the animal 
lives, and which communicate this wave motion to the nerves 
connecting them with the brain. Do we really meet with this 
condition of things in the auditory organ? In other words, is 
the auditory organ merely a specially modified portion of the 
system of segmental sense organs ? 
The auditory organ is, like the segmental sense organs, really 
a modified portion of the epiblast. Very early in development it 
becomes shut off in a sac from the epidermis, a condition which 
only arises later in the segmental sense organs. 
Phe semicircular canals, etc., are clearly secondary compli- 
cations, for in every embryo the auditory organ is at first a 
simple sac shut off from the epidermis, of which sac a portion of 
the inner wall consists of two layers of modified epiblastic cells, 
connected by a dorsal sensory branch of a segmental nerve with 
the brain. 
© This double layer of modified epiblastic cells is in every way 
— . ON 
