Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 84 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. sciousness as a specific .sensation. To these end-cells there are often added cuticular structures, whose function is to communicate the external movement to the nervous substance (retinal rods). The special sensations have quite gradually been developed from the general sensations (comfort, discomfort, pleasure, pain), , nerves of special sense have been derived from sensory nerves which have acquired a special form of periphera
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 84 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. sciousness as a specific .sensation. To these end-cells there are often added cuticular structures, whose function is to communicate the external movement to the nervous substance (retinal rods). The special sensations have quite gradually been developed from the general sensations (comfort, discomfort, pleasure, pain), , nerves of special sense have been derived from sensory nerves which have acquired a special form of peripheral termination, and so become accessible to a special stimulus with which the special sensation is always associated. But it is not till a higher stage of development is reached that the sense-perceptions can be compared according to the nature of the sensations with those of our own body. We can estimate the sense energies of the lower animals exceedingly vaguely, and only by the insufficient method of com- paring them with our own sensations; and it is certain that among the lower ani- mals there are many forms of sensation of which we, in consequence of the spe- cialised nature of our own senses, can have no concep- tion. Probably of all the senses, that of touch is the most widely distributed, and with this we certainly often see a number of special sensations united. It is generally distributed , over the whole surface of the body ; frequently, however, it is con- centrated on processes and appendages of it. Probably the tentacular appendages of the Coelenterata and Echinodermata have this signifi- cance. In the Bilateralia with a differentiated head there are contractile or stiff segmented processes on the head, the antennce or feelers which in the worms are repeated as paired cirri on every segment of the body. It is often possible to trace special nerves to the skin and to find touch organs containing their endings. In the Arthropoda the ganglionic end-swelling of a tact
Size: 1375px × 1454px
Photo credit: © Bookworm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
