""jg^j^ J Cuckoos and Migration in Birds. l47 



of development in which it is successively similar in form or i)ro- 

 portion of parts to a higher and still higher animal, till it attains 

 the form of its species. Numerous parallelisms support this view. 

 Most animals have a tendency to move about and their organs to 

 react in definite ways to definite stimuli before there is any chance 

 to experience their favourable or unfavourable character even in 

 a slight degree. This presupposes an outside stimulus. If such a 

 stimulus be not given and received the object is immobile, and 

 consequently inactive, notwithstanding that the latest investiga- 

 tions seem to show that matter itself is life. It is therefore 

 necessary for matter or an object to receive a " primary " stimulus 

 to move and blossom forth into life or action. It is the stimulus 

 that governs the movement, not the movement that controls the 

 stimulus — at least, not the primary stimulus — hence one cannot 

 classify a stimulus as an instinct. By human analogy we find that 

 a person sleeping in bed will, on receiving a certain stimulus, roll 

 over in bed into a more comfortable position without awaking 

 from his or her unconsciousness. Can this be attributed to instinct ? 

 Then, again, an analogous case is the migration of birds, in which 

 climatic conditions, apart from food and other conditions, bring 

 about the unfavourable stimulus or stimuli from which the birds 

 move to places where the stimuli are absent or modified. Were 

 there no seasons in the year birds would remain in the one place, 

 and would lose their migratory habits, provided other unfavourable 

 stimuli were absent. Hence we find the permanent stimuli of the 

 seasons and their reflex actions causing migration always at the 

 same season of the year, and mostly in the same direction, the 

 date of migration varying according to the climatic condition of 

 the season. This leads one to the supposition that migratory birds 

 are of a delicate constitution, which, for their survival, causes them 

 to shrink from the rigorous climatic conditions that cause unfavour- 

 able stimuli, and travel to suitable zones. The summar}/ of the 

 above necessarily condensed points suggests that the action of the 

 young Cuckoo is a rhythmic one, an organic and automatic tendency 

 even more fundamental than an instinct, and that there is no line 

 of demarcation between instinct and reason, as 1 will proceed to 

 exemplify. Replace the young Cuckoo in the nest, and exactly 

 the same process is repeated again and again, with a rhythmic 

 precision. Were there no other fellow-nestlings with the young 

 Cuckoo there would be no iritating stimulus, consequently there 

 would be no reactionary movements. Many reactionary move- 

 ments caused by one kind of stimulus are dependent on other 

 stimuli acting in conjunction with them. For instance, the jxn- 

 manent stimuli of the legs attached to the young Cuckoo cause it 

 to rear up or erect itself in the nest in response to the j^rimary and 

 intermediary stimuli. These stimuli are so co-ordinated and 

 dependent on one another tliat one can easily trace the details ol 

 the ejective action caused by the primary stimuli, and the reaction 

 of that force, together with that of the stimuli of light, with which 

 are combined the stimuli of air temperature or air movement 



