6 
PRESIDENT'S ADDRESS. 
the sense impressions received. Even in such a lowly member 
of the series as the Jelly Fish the first dawn of sight and other 
special sense-organs was discernible. In the Platyhelminthes 
and other worms there was ample evidence of further evolution 
in the complexity and development of a nervous system, till 
we reached the Molluscs, who are very richly endowed in this 
respect. Dr. Thomson pointed out the evidences of the 
sense of sight in the Oyster and other molluscs, notably in 
the active and predatory Octopus or cuttle-fish, whose eye- 
sight, for example, is as well developed as that of a fish at 
least, and falls not far short of that of man. It was also 
demonstrated by many interesting instances that eyesight 
is developed proportionately to the animal’s power of loco- 
motion, as in the Hawk, a swift and keen-sighted bird. In 
the Arthropoda, or highest phylum of Invertebrates, there is 
further evolution and complicacy of the nervous system. 
The Arthropoda comprise the spiders and insects, and the 
marvellous instincts of these creatures give ample evidence 
of the very high evolution of their sense organs and nervous 
system generally. The anatomy and physiology of the simple 
and compound eye of insects were explained, how the com- 
pound eye of the blowfly does not see, say, a thousand 
separate inverted images, but a single “ right-side-up ” 
picture, or mosaic, as it were. Dr. Thomson then passed on 
to the Vertebrata, or back-boned animals, comprising fishes, 
amphibians, reptiles, birds, and mammals. Here the same 
serial complexity and gradually higher evolution were evident, 
and traced by the lecturer with the aid of lantern slides and 
diagrams. He pointed out, however, that an apparently new 
departure in plan of the nervous system of Vertebrates began 
to be evolved, viz., instead of the “ diffuse,” “ linear,” and 
“ ganglionic ” arrangements met with in Invertebrates, 
usually situated in the under, or ventral, region of the animal, 
there began to be evolved a “ cerebro- spinal axis ” in the 
dorsal or backbone region. It was shown how from fishes 
