August 22, 1S95] 



NA TURE 



389 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can lie undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. ] 



The University of London. 



Mr. TillsEi ion-Dvek now narrows his attack to my sug- 

 gestionthatin voting on the new Charter, membersof Convocation 

 should do so " as at a Senatorial election," i.e. by voting papers. 

 This seems a very narrow basis for so severe a condemnation. 



The reason for this provision was, I presume, that as many 

 members of Convocation are professional men, masters of 

 schools, &c. , it is in many cases difficult, if not impossible, for 

 them to come up to London. 



The provision applies, I may add, not only to Senatorial, but 

 aJso to Parliamentary, elections. I cannot see why Mr. 

 Thiselton-Dyer should assume thai a vote so taken would 

 " destroy the prospects of academic study in London." That, 

 however, is not an attack on me, but on the Constituency. 



High Elms, August 17. John Lubbock. 



Plant-Animal Symbiosis. 



In I'rof. Stewart's collection at the Royal College of Sur- 

 geons there is a preparation of a mimosa which protects itself 

 from browsing animals by providing in its great thorns a 

 <lomicile for a species of vicious, stinging ants. I believe 

 this example of plant-animal symbiosis comes from one of 

 the West Indian Islands, while on the mainland of .\merica the 

 same species of mimosa exists, but suffers greatly from the depre- 

 <lations of animals, because there is no suitable ant to come and 

 ward them off. If my recollection of the distribution is correct, 

 the following note of a similar phenomenon in South Africa, I 

 think, is of considerable interest. 



In a recent tour through the Karroo, in search of the skeleton of 

 the Dicynodons, I came across a mimosa tree which here forms the 

 chief fuel, on one of the lower branches of which there were some 

 very large thorns ; one of these had a little oval hole bored just 

 beneath the summit. On breaking it open, there issued an in- 

 credible number of ants, considering that they were packed in 

 the space of a pair of spines about four inches long and half an 

 inch in diameter. The asexual forms were of the usual two 

 kinds : the soldiers were about a quarter of an inch long, brown, 

 and very attenuated, showing very markedly the influence of 

 surroundings on form ; while the workers were scarcely half the 

 size of their protectors, and of a darker hue. The sexual forms 

 I did not see. The ants emerged from the crack in a very sleepy 

 manner, and did not seem at all aggressive ; this may have been 

 on account of the cold, which w'ould affect them more than their 

 relatives which live in the earth. Embeclded in the soft wood of 

 the stem, where the two spines meet, were several aphides, which 

 thus were able to feed themselves on the sap of the tree, and 

 yet always be within the house of their owners. In the West 

 Indian thorn-tree the leaves offer a further inducement to the 

 ants to remain constantly near them, by providing at the ex- 

 tremity of the leaflets little masses of a nutritious substance 

 adapted to the digestions of their guests ; in the South .African 

 tree there is a mass situate at the base of the leaves, similar to 

 that in the cherry, which probably serves the same object. On 

 returning shortly afterwards, I found the ants had trekked with 

 all their cattle, and I failed to trace their whereabouts. The 

 locality w.as the gold-fields of Spreeunfontein, in the Prince 

 Albert district. Ernkst H. L. Schwarz. 



Ca|x; Town, August i. 



Definitions of Instinct. 

 1 HAVE read with interest the abstract of Mr. C. W. Purnell's 

 paper which you published in last week's Naurk (p. 383). I 

 think he is in error in supposing that young birds do not afford 

 I's examples of truly instinctive activities. The way in which a 

 young moorhen swims with accurate coordination, before the 

 •down is well dry after hatching, and before it can walk steadily, 

 is very instinctive. I would suggest to Mr. Purnell that there 

 IS a wide field for observation open to him among his native 

 birds. If he will hatch some of them out m the incubator, and 

 carefully note what they can do prior to experience, and how 

 their activities are modified by experience, he will help to solve 

 iome of the difficult problems of habit and instinct. 



NO. 1347, VOL. 52] 



I have myself advocated a restriction in the meaning of the 

 term somewhat similar to that for which he argues. I shall be 

 obliged if you can find space for the provisional scheme of 

 terminology thus suggested in Natural Science for May 1895, 

 w hich I have since somewhat extended and amended. To bring 

 it into line w ith modern biological thought, a good deal of stress 

 is laid on the question of heredity, and on the distinction be- 

 tween the definiteness which is congenital and that which is ac- 

 quired. It may be premised : 



( 1 ) That the terms congenital and act/uired are to be regarded 

 as mutually exclusive. "VVhat is congenital in its definiteness is, 

 as prior to individual experience, not acquired ; the definite- 

 ness that is acquired is, as the result of individual experience, 

 not congenital ; 



(2) That these terms apply to the individual. Whether what 

 is acquired by one individual may become congenital through 

 inheritance in another individual, is a <juestion of fact which is 

 not to he settled Ijy implications of terminolog)' : 



(3) That the term acijuired does not exclude an inherited 

 potentiality of acquisition under the appropriate conditions. 

 Such inherited potentiality may be termed innate. WTiat is 

 acquired is a definite specialisation of an indefinite innate 

 potentiality ; 



(4) That what is congenital and innate is inherent in the 

 germ-plasm of the fertilised ovum. 



Congenital mo^'cments and activities : those the definite 

 performance of which is antecedent to individual experience. 

 They may be performed either (i) at or very shortly after birth 

 (connate), or (2) when the organism has undergone further 

 development (deferred). 



Congenital automatism : the congenital physiological basis of 

 those movements or activities the definite performance of which 

 is antecedent to individual experience. 



Thysioirgical rhythms : congenital (and connate) rhythmic 

 movements essential to the continuance of organic life. 



Reflex moz^ements : congenital, adaptive, and coordinated 

 responses of limbs or parts of the body : directly evoked by 

 stimuli. 



Random movements : congenital, more or less definite, but 

 not specially adaptive movements of limbs or parts of the body ; 

 either centrally initiated or directly evoked by stimuli. 



Instinctive activities: congenital, adaptive, and coordinated 

 activities of relative complexity, and involnng the welfare of the 

 organism as a whole ; specific in character, but subject to varia- 

 tion analogous to that found in organic structures : similarly 

 performed by all the members of the same more or less re- 

 stricted group, in adaptation to special circumstances frequently 

 recurring or essential to the continuance of the race ; often 

 periodic in development and serial in character. 



Imitative movements and activities: due to individual 

 imitation oi similar movements or activities performed by 

 others. 



Impulse ( Trieb) : the affective or emotional condition, whether 

 congenital or acquired, under the influence of which a conscious 

 organism is prompted to movement or activity, without reference 

 to a conceived end or ideal. 



Instinct: the congenital psychological impulse concerned in 

 mstinctive activities. 



Control: the conscious inhibition or augmentation of move- 

 ment or activity. While the power of control is innate, its 

 special mode of application is the result of experience, and 

 therefore acquired. 



Intelligent activities: those due to individual control or 

 guidance in the light of experience through association (volun- 

 tary). 



Motive: the affective or emotional condition under the in- 

 fluence of which a rational being is guitled in the performance 

 of deliberate acts. 



Deliberate acts: those performed in distinct reference to a 

 conceived end or ideal (volitional). 



Habits : organised groups of activities, stereotyped by rejieti- 

 tion, and characteristic of a conscious organism at any particular 

 stage of its existence. 



Acquired movements, activities, and acts : those the definite 

 performance of which is the result of individual experience. Any 

 modifications of congenital activities w hich result from experience 

 are, so far, acquired. 



Aci/uired automatism : the individually modified physiological 

 basis of the performance of those acquired movements or activities 

 which have been stereotyped by repetition. 



C. Li.oYD Morgan*. 



