ON THE ORIGIN OF THE VERTEBRATE 
SENSE ORGANS. 
BY: H. V. WILSOM: 
The belief that the chief sense organs of vertebrates 
have been evolved from a longitudinal series of simple 
and superficially situated organs rests on morphological 
evidence, which 1f not conclusive is yet very considerable. 
Beard’ in 1885 described in selachian embryos a series 
of rudimentary sense patches (ectodermal thickenings), 
on eabove each gill cleft. These he termed the branchial 
sense organs. Similar organs have been found by Beard 
and several observers (Froriep, Kupffer etc.) in the em- 
bryos of other Ichthyopsida, birds, and mammals. It 
may be confidently asserted that a phylogenetic signifi- 
cance attaches to these formations, and that the ancestors 
of existing vertebrates had a series of sense organs (two 
series, one more dorsal than the other: Kupffer) situated 
in the anterior (branchial) region of the body. 
The sense organs of the lateral line, and of the mucus 
canals of the head, found in adult fishes, tailed amphibia, 
and in anuran larvae, are known to arise by the prolifer- 
ation of the above mentioned embryonic organs, which 
thus became extended far beyond the seat of their origi- 
nal appearance. 
The position and mode of origin of the embryonic nasal ° 
and auditory invaginations led Beard to regard these or- 
vans as homologous with his series of branchial sense or- 
gans. And this conclusion has been in general. accepted 
by later investigators. | 
It might some years ago have seemed impossible to in- 
1Branchial Sense Organs of Ichthyopsida. Quart. Journ. Micr, Sci, 
1885, 
