Licence: Public Domain Mark
Credit: Documents and dates of modern discoveries in the nervous system. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
38/192 (page 22)
![largest brain in proportion to the nerves given off from it, and that this proportional magnitude may, in every instance, be referred to as the best criterion of the degrees of intelligence. Now it appears to me not at all difficult to account for this fact (the general truth of which may be granted) by com- paring it with another not less important, viz. that, in the inferior classes of animals, the nervous system becomes, as we descend, more and more widely diffused. Now the more equally distributed this system is, the more independent of each other are the parts of organised beings. Animals having this sensitive substance very gene- rally diffused, when mutilated, recover their figure, or when cut into pieces, form several individuals, having each a system of sensation and volition. Animals having this system perhaps generally dif- fused, as the polyp, having been divided into the smallest fragments, each fragment self exists, and becomes a perfect individual. Yet these polyps, thus minutely divisible and des- titute of perception, have great sensibility. Their sense of touch is exquisite, and they not only feel the slightest motion of water, but all the degrees of heat and light. To the last of these the hydra is very sensible, as it always turns to it, and seems to enjoy it. The Actiniae also expand in exact corres- pondence to the serenity of the atmosphere. The sensibility of these animals [some worms] is](https://iiif.wellcomecollection.org/image/b21721804_0038.jp2/full/800%2C/0/default.jpg)
