DESIGN IN NATURE 



244 



It goes without saying that the ant, the bee, the spider, and the bird cannot build their nests and carry on their 

 domestic economy as apart from conscious thought any more than men can build houses and cities and institute 

 governments as apart from conscious intelhgent effort. If consciousness and intelligence withm hmits be demed 

 the ant the bee, the spider, and the bird, then it is obvious that these attributes must be exercised by the Creator 

 in and through them. The nest of the ant, the honeycomb of the bee, the web of the spider, and the nest of the 

 bird are constructed with surpassing skill. They are, in no sense, chance products. On the contrary, they are 

 paragons of workmanship and design, and the highest resources of mathematics, physics, and mechamcs are not 

 unfrequently laid under contribution. Consciousness and intelligence are, though to a less degree, present in their 

 case as they are in man. It is mere evasion to say that an ant, a bee, a spider, and a bird bmld their nests exclu- 

 sively by instinct, and that a man builds his houses and cities wholly by conscious intelhgent effort. The distinction 

 is altogether artificial. As there is no difference in the nerve substance of the lower and higher ammak, and no 

 breach of continuity in the chain which connects the one with the other, it is evident that what holds true of the 

 highest animals also holds true, within limits, of their lower congeners. . , , 



I have to express my conviction that conscious reasoning power can be traced in all the lower ammals where, 

 in their workings, they provide examples of the adaptation of means to ends. Similar remarks are to be made 

 (but in a modified and lower sense) of plants, where no differentiated nervous system exists. The presence of a 

 nervous system, as we know it, is not necessary to adaptation, and the arranging of means to ends. 



The subject of instinct raises the important question of reflex nerve action as it exists in the higher ammals 

 and in man. As is well known, the nervous system in man is divided into two parts : the cerebro-spinal part, con- 

 sisting of the brain and the spinal cord plus the sensory and motor nerves, and the sympathetic part, consisting of a 

 double chain of nerve ganglia extending on either side of the vertebral column plus visceral and other nerve plexuses. 

 These two parts are united to each other at various points ; the nervous system in reality being a continuous whole. 

 There is this pecuharity. The voluntary movements of the body are controlled by the cerebro-spinal portion : the 

 involuntary, for the most part, by the sympathetic portion. The modus operandi of the cerebro-spinal system is 

 usually as follows. A sensation due to some external object is transmitted from the peripheral sensory nerves which 

 travels inwards to the ganglia of the spinal cord, and thence to the gangha of the brain, where it is perceived and 

 interpreted. The brain in turn sends an impulse, which travels outwards by the motor nerves to the muscles which 

 are set in motion. The brain can act independently from within, as apart from sensations or impulses transmitted 

 from without. In other words, the brain, or the mind acting through it, can originate motor impulses similar in 

 some respects to the sensory impulses transmitted by the sensory nerves and the sense organs. In the case of a 

 reflex nerve action the sensation, as a rule, only reaches the ganglia of the spinal cord, where it is perceived and inter- 

 preted ; a motor impulse being generated and sent on to the muscles by the motor nerves without the knowledge 

 or co-operation of the brain. The reflex act does not involve voUtion and consciousness in the ordinary sense. It 

 may occur in the decapitated frog and in man where the brain or the upper part of the spinal cord are diseased, and 

 where they are functionally cut off or disassociated from the spinal cord as a whole. In such cases, the reflex act 

 may be largely explained by a nerve habit acquired by constant repetition of acts performed by the entire cerebro- 

 spinal system during the Ufe of the individual : the spinal cord and sensory and motor nerves being taught to 

 perform their parts independently of the brain. 



The nerve-habit due to the repetition of certain acts becomes after a time automatic, and when once estab- 

 hshed forms what may be regarded as part of a self-acting machine, which when once set in motion is inchned to 

 go on indefinitely. This is true of nerve reflexes generally, and of the nerve and muscular arrangements of the 

 heart, lungs, alimentary canal, bladder, uterus, &c. 



The nerve-habit in the higher animals is almost invariably associated with a muscular habit, and it is often 

 exceedingly difficult to distinguish between the two. The nerves and muscles, as a rule, act conjointly, but they 

 also, as will be seen further on, act singly and independently. The brain by its motor nerves may send impulses to 

 the muscles of an amputated or paralysed limb. Similarly, the heart may act without its nerves and as apart from 

 the brain. The heart of the chick is composed of a mass of nucleated cells with no trace of either nerves or muscles, 

 yet the organ acts perfectly. 



If the sensory nerves be diseased or from any cause paralysed, no sensations reach the brain, and if the motor 

 nerves be similarly circumstanced no motor impulses reach the muscles. The self-acting machine formed by the 

 co-ordinated movements of the nerves and muscles must be intact for the performance of cerebro-spinal voluntary 

 acts. In the case of reflex nerve acts it suffices if a portion of the self-acting machine is unimpaired and in perfect 

 working order. 



The point of transcending interest in this connection is the relation of the reflex nerve acts of the higher 

 animals to the nerve acts witnessed in the lower animals having a nervous system (with or without a brain) ; it being 



