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taken up by the lateral nerve formed from the vagus complex. This 
change was probably assisted by an anastomosis between some of the 
terminal fibres of neighbouring dorsal sensory branches. Some remains 
of this anastomosis perhaps still exist in the fibres described by 
Bodenstein and Solger as connecting neighbouring sense organs. 
Thus it appears that in Vertebrates there are segmental sense 
organs or Seiten-Organe which were primitively innervated by special 
segmental branches of the segmental nerves, that many of these special 
branches have disappeared, and the innervation has become complex; 
but that in the segmental character of the organs, in the persistence of 
many of the dorsal branches supplying these organs, in the conditions 
of nerve supply obtaining in embryonic Elasmobranchii, and in the 
essential histological agreement between the Vertebrate side organs and 
those of Annelida, especially Capitellidae (Eisig), there seems to be 
evidence sufficient for the opinion, first put forward by Eisig, that the 
Vertebrate side organs and those of Annelida are fundamentally homo- 
logous. 
It is perhaps hardly necessary to point out the value of such a fact 
in supporting the theory of the Annelidan origin of Vertebrates advo- 
cated by Dohrn and Semper. 
Morphology of the Vertebrate auditory organ. 
Before concluding this »Vorläufige Mittheilung« attention must be 
directed to another Vertebrate sense organ, the ear. 
The chief vertebrate sense organs have certainly had a very diffe- 
rent origin. The olfactory organ is probably a modified gill (Mar- 
shall). The eye is developmentally and really part of the brain. Such 
a view was also once held with regard to the 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 (3rd seg- 
mental nerve of Van Wijhe). 
It has been shown above that the nerves which supply the seg- 
mental sense organs are dorsal sensory branches of the segmental 
nerves, that the segmental sense organs are merely modified portions 
of the epiblast, that these sense organs primitively, and in some exist- 
ing 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 
