TRANSACTIONS OJ<' THE SECTIONS. 135 



iu -wliicli an animal closely resembled either some part of a plant or some 

 inorganic object ; and expressed the opinion that these two sets of cases were 

 wholly one iu kind, the evident object iu all being the protection of the imitator. 

 Describing a visit paid to the vicinity of Grahamstown in search of this insect, he 

 observed that it was a work of considerable difficulty to distinguish the gi-asshoppers 

 from the stones, and he was engaged for half an hour in careful search over a known 

 station of the species before discovering an example. lie noted the further most 

 interesting fact, that, in certain spots (often only a few square j-ards iu extent) 

 ■where the stones lying on the ground were darker, lighter, or more mottled tlian 

 those generally prevalent, the Trach/petra found among such stones varied similarly 

 from the ordinary dull ferruginous-brown colouring in imitation of them. It was 

 pointed out that the close imitation of the stones was mainly effected by the modi- 

 fication of the dorsal shield of the prothorax, which is (with the whole thorax) much 

 flattened and widened, and is fm-ther much produced posteriorlj^, and has its sur- 

 face roughened or granidated in close resemblance to the surface of the stones. 



In conclusion, he called attention to the bearing of the case of tliis insect on the 

 question of the origin of species ; and iu putting the alternative whether the pe- 

 culiar station of the Trachypetra had been specially prepared for it immediately 

 before or simultaneously with the creation of the insect, or whether, on the contrary, 

 the insect had Ijeen very gradually modified by natural selection in imitation of the 

 stones for the pm-pose of concealment, he expressed his decided opinion in favour of 

 the latter hypothesis. 



Specimens of the insect were exhibited in association with some of the stones 

 among which they were captured ; aud the very close resemblance between the 

 stones and the insects was very obvious. Mr. Trimen observed that in nature the 

 mimicrj' was more effective, the colours of the dead insects having faded consider- 

 ably, and the shrinking of the abdomen having caused the hind legs to be much 

 more apparent than was the case in living examples. 



Les CJiauves-souris de Tepoque du Mammouth et de Vepoque actuelle. 

 Par Professeur Van Beneden. 



La thi^orie de Darwin est, dit-on, une veritable conception scientifique, fondee 

 8ur la concurrence vitale et la selection naturelle. L'evohitiou uaturelle des 

 formes est pour le savant illustre le r6sultat de la lutte pour la vie et de la sm-- 

 vivance des plus forts. 



Si les animaux subissent la loi de cette concurrence vitale et de la stSlection 

 naturelle, il faut se demander quel est I'effet de cette influence pendant la piSriode 

 actuelle. 



Pendant ce long laps de temps qui nous si^pare de I'age du Mammouth et de 

 rOiu's des cavernes, quelles sont les modifications qui sont survenues dans le nombre 

 comme dans les caracteres des especes ? S'aperfoit-on des effets de la lutte pour la 

 vie et, comme consequence, de la survivance des plus forts ? C'est la question que 

 nous avons voulu examiner. 



On est generalement d'accord sur ce point que, pour expliquer les ph<5nomene8 

 des temps g^ologiques, il faut chercher la solution dans les phi^uomenes de I'epoquo 

 actuelle. Ce qui se passe sous nos yeux doit nous fairo comprendre ce qui s'est 

 pass6 anterieurement. 



C'est cette pensee que vient d'exprimer avec tant d'eMgance I'illustre President 

 de 1' Association, Sir William Tliomson, dans son discours d'ouverture : L'essence 

 de la science consiste a d(§duire de ph6nomenes actuellemeut soumis a I'observa- 

 tion I'etat anterieur des choses, et a prejuger lem-s evolutions futures. 



Nous avons eti conduit a nous occuper de ces questions a la suite de recherches 

 sm'les parasites des Oheiropteres (Chauves-somis) et d'explorations faites dans les 

 cavernes. Nous avons compare des animaux, vivant autour de nous et dans nos 

 grottes, avec ceux qui hantaient autrefois ces memes lieux a I'epoque oil les Ours 

 et les Rennes remplissaient ces retraites de leurs depouilles. 



L'on salt que les ossements qui sont enfouis avec ceux des Ours appartiennent a 

 trois categories d'animaux : la premiere comprend ceux qui out disparu de nos 



