The Outline of Science, Volume 1

Simple creatures act with a certain degree of spontaneity on their environment, and they likewise react effectively to surrounding stimuli. Animals come to have definite "answers back," sometimes several, sometimes only one, as in the case of the Slipper Animalcule, which reverses its cilia when it comes within the sphere of some disturbing influence, retreats, and, turning upon itself tentatively, sets off again in the same general direction as before, but at an angle to the previous line. If it misses the disturbing influence, well and good; if it strikes it again, the tactics are repeated until a satisfactory way out is discovered or the stimulation proves fatal. It may be said that the Slipper Animalcule has but one answer to every question, but there are many Protozoa which have several enregistered reactions. When there are alternative reactions which are tried one after another, the animal is pursuing what is called the trial-and-error method, and a higher note is struck. There is an endeavour after satisfaction, and a trial of answers. When the creature profits by experience to the extent of giving the right answer first, there is the beginning of learning. DIAGRAM OF A SIMPLE REFLEX ARC IN A BACKBONELESS ANIMAL LIKE AN EARTHWORM 1. A sensory nerve-cell (S.C.) on the surface receives a stimulus. 2. The stimulus travels along the sensatory nerve-fibre (S.F.) 3. The sensory nerve-fibre branches in the nerve-cord. 4. Its branches come into close contact (SY1) with those of an associative or communicating nerve-cell (A.C.). 5. Other branches of the associative cell come into close contact (SY2) with the branches or dendrites of a motor nerve-cell (M.C.). 6. An impulse or command travels along the motor nerve-fibre or axis cylinder of the motor nerve-cell. 7. The motor nerve-fibre ends on a muscle-fibre (M.F.) near the surface. This moves and the reflex action is complete. Photo: British Museum (Natural History). THE YUCCA MOTH The Yucca Moth, emerging from her cocoon, flies at night to a Yucca flower and collects pollen from the stamens, holding a little ball of it in her mouth-parts. She then visits another flower and lays an egg in the seed-box. After this she applies the pollen to the tip of the pistil, thus securing the fertilisation of the flower and the growth of the ovules in the pod. Yucca flowers in Britain do not produce seeds because there are no Yucca Moths. INCLINED PLANE OF ANIMAL BEHAVIOUR Diagram illustrating animal behaviour. The main line represents the general life of the creature. On the upper side are activities implying initiative; on the lower side actions which are almost automatic. Upper Side.—I. Energetic actions. II. Simple tentatives. III. Trial-and-error methods. IV. Non-intelligent experiments. V. Experiential "learning." VI. Associative "learning." VII. Intelligent behaviour. VIII. Rational conduct (man). Lower Side.—1. Reactions to environment. 2. Enregistered reactions. 3. Simple reflex actions. 4. Compound reflex actions. 5. Tropisms. 6. Enregistered rhythms. 7. Simple instincts. 8. Chain instincts. 9. Instinctive activities influenced by intelligence. 10. Subconscious cerebration at a high level (man). Photo: J. J. Ward, F.E.S. VENUS' FLY-TRAP One of the most remarkable plants in the world, which captures its prey by means of a trap formed from part of its leaf. It has been induced to snap at and hold a bristle. If an insect lighting on the leaf touches one of six very sensitive hairs, which pull the trigger of the movement, the two halves of the leaf close rapidly and the fringing teeth on the margin interlock, preventing the insect's escape. Then follows an exudation of digestive juice. [Pg 77] Reproduced by permission from "The Wonders of Instinct" by J. H. Fabre. A SPIDER SUNNING HER EGGS A kind of spider, called Lycosa, lying head downwards at the edge of her nest, and holding her silken cocoon—the bag containing the eggs—up towards the sun in her hindmost pair of legs. This extraordinary proceeding is believed to assist in the hatching.