tA.6 Mattingley, Priticiplcs Governiiig Movctneiil in 1,^, "j"„ 



Hence, to simplify matters, it would be advisable to systematically 

 go to the root of the matter at issue and more clearly and closely 

 outline the correctness of my contention. The action of the young 

 Cuckoo in ejecting its fellow-nestlings is a guiding propensity or 

 physiological law — a rhythmic action which is really an organic 

 and automatic tendency more fundamental even than instinct — 

 and, moreover, instinct and reason are not divisible into separate 

 powers, there being no line of demarcation between them. First it 

 will be necessary to clearly define instinct and reason, and by illus- 

 trations and hypotheses to prove that neither of these powers is 

 operating at the time, and that they do not in any way govern 

 the ejectment. The word instinct is derived from the Latin 

 instinguere, to excite. From a stimulus or exciter an impulse is 

 derived, but can we call a stimulus or an impulse an instinct ? We 

 should seek for every other explanation before using a word so 

 comprehensive, indefinite, and apt to mislead. In all life there are 

 two kinds of stimuli, the permanent and the fortuitous. That 

 which is permanent is born with the animal, and that which is 

 fortuitous is derived externally. The permanent stimulus is in- 

 herited, and therefore never erring. Can we logically assume that 

 it is instinct that causes the spermatozoon to enter the ovum, or 

 the pitcher plant to close around a fly and thus entrap it ? There 

 is no doubt that certain organisms come into play later on as they 

 become more fully developed, but at this period of the Cuckoo's 

 life-history (a few hours old) these organisms are not developed 

 sufficiently to transmit the power or faculty known as instinct, 

 implying the degree of knowledge. Instinct and reason are merely 

 different stages of development running into one another by such 

 imperceptible degrees that it is impossible to draw a line of 

 demarcation. The same applies to the stages of development and 

 metamorphoses of the cells until they arrive at the requisite 

 organisms which convey the faculty of instinct or reason. 



The principles determining the order of development of instinct 

 as instanced in the plant world, where leaves, stalk, blossom, and 

 fruit follow one another, are definite and fixed. In the animal 

 world the growth of parts of the body and the appearance of hair, 

 horns, teeth, feathers, beak, &c., are nearly as fixed and unvarying. 

 Since structure and instinct are closely related, we should expect 

 to find a definite order in which the instincts of each species of 

 animal tend to develop. Observation confirms this view in a general 

 way, as young birds do not show the mating, nest-constructing, 

 and caretaking instinct or reason of adult birds, nor do adult birds 

 show the same degree of playfulness as younger birds. 



When, however, we attempt to determine exactly the order in 

 which instinct or reason develops, many doubts and difficulties 

 arise. The most common theoretical statement is that instincts 

 develop in that order in which they have been acquired in the 

 history of the race, built as all species are from the lowest forms of 

 the genus upwards. This view is supported by a general biological 

 law, that in the embryonic state each animal goes through stages 



