s.c. 



NER_VE__CORD_ 



DIAGRAM OF A SIMPLE REFLEX ARC IN A BACKBONE- 

 LESS 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 (SY 1 ) with those of 

 an associative or communicating nerve-cell (A.C.). 



5. Other branches of the associative cell come into close con- 

 tact (SY 2 ) 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 fertil- 

 isation 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. I. 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 in- 

 fluenced by intelligence. 10. Subconscious cerebration at a high level (man). 



