ELISHA MITCHELL SCIENTIFIC SOCIETY. 57 
clude the eye in this lateral series of homodynamous or- 
gaus. But while the eyes (optic vesicles) ordinarily orig- 
inate as diverticula from the fore-brain, it 1s now known 
that in many forms they make their appearance as invag- 
inations of the surface ectoderm, long before the neural 
folds have closed. In this condition the optic vesicle is a 
circular depression, substantially like the auditory or 
nasal pit. . Later these depressions are carried inwards 
with the invaginating neural plate, and then appear as 
outgrowths of the brain. ‘The early appearance of the 
optic vesicles has long been known in mammals, but until 
within recent years it has been regarded as a peculiar 
and precocious feature of this group. Through the ob- 
servations of Whitman’, Eyclesheimer’, and Locy', we 
have learned that the optic vesicles originate in this man- 
ner in several amphibia, in selachians, and the chick. 
These observations at least lend us a basis for the com- 
parison of the eyes with the other segmentally arranged 
sense organs, and meantime (Locy lc. p. 556) ‘‘we are in 
the attitude of awaiting further facts.” 
The scattered integumentary sense organs (taste buds, 
touch corpuscles) have not been shown to be derived from 
anlages, serially homologous with the anterior segment- 
ally arranged series. 
The derivation of the chief vertebrate sense organs 
from a longitudinal series of superficial neuro-epithelium 
patches, might at first thought be construed into a sound 
argument for the annelid-theory of vertebrate ancestry. 
But when it is borne in mind that the vertebrate series 
is, in the embryo, confined to the anterior (branchial) re- 
gion, whence the organs spread back over the trunk and 
forwards over the head by proliferation, it will be recog- 
2Journal of Morphology, 1889, p. 593. 
3Journ. Morphology, 1893, Vol. VIII, No. 1, p, 189. 
4Contributions to the Structure and development of the Vertebrate 
Head. Journ, Morphology, 1895, 
