86 



NA TURE 



[May 25, 1882 



movement. A cover over all keeps the light out from the 

 rear of the instrument. It will be noted that during the 

 instant of exposure, the sensitised surface is steady, and 

 when the exposure is over, it is at once passed away. 

 Pressure on the button (b, Fig. 2, 1) sets the machine in 

 motion. Before applying this instrument to the study of 

 the flight of birds, an experiment was made with it on a 

 black arrow, made to rotate against a white back ground 

 well lit up. The speed of the rotation of the arrow was 

 about 5 metres a second. The marksman, at a distance 

 of 10 metres sighted on the centre of the target, on 

 which the eye could perceive nothing save a confused 

 grey shadow, so quick was the rotation of the arrow : but 

 on the development being complete .1, twelve images were 

 to be seen, disposed in a circular manner, and each showed 

 not only the arrow, but its shadow, as sharp as if the 

 original had been immovable. Another experiment, 

 equally successful, was made on a pendulum beating 

 seconds. For to be more certain as to the duration of the 

 exposure, M. Marey next adapted to the gun a chrono- 

 graphic apparatus, so that the time intervening between 

 the taking of each picture could be with precision ascer- 

 tained. After all these preliminary essays, the photo- 

 graphy of animals in movement was attempted; and in 

 Fig. 3 there will be seen the photographic representations of 

 a sea-gull, in which the twelve successive attitudes assumed 

 during the space of a single second by this bird during 

 flight are ascertained. On other occasions other succe^s- 



Fig. 5. — Si;::-gull ; end of depress) n of wing. 



ful photographic series of a sea-gull in flight were taken 

 when the bird was seen less in profile. The sea-gull gave 

 exactly three strokes of its wing each second, so in the 

 twelve photographs of each stroke four succeeding stages 

 were reproduced. The wings at first elevated to their 

 greatest; then commence to be lowered ; then in the follow- 

 ing image they are seen at the lowest point of their course ; 

 and in the fourth image are again on the rise. In enlarg- 

 ing these images, figures seen from a good distance were 

 obtainable, but the sharpness of the enlargements left a 

 good deal to be desired ; for the negatives were somewhat 

 granular, no doubt owing to some slight fault in the 

 photographic process. The reproduction of these images 

 by the heliographic process gives excellent silhouettes (as 

 seen in Figs. 4 and 51 ; the originals, when examined 

 under the microbe jpe, showed even the wing-feathers 

 distinctly. 



On compaiing the indi rations thus given by the photo- 

 graphic process with those already attained by the graphic 

 process, a confirmation o : most of the principal points 

 obtained by the latter were obtained ; but otherwise so 

 far, the latter did not seem to add much to our know ledge 

 of the mechanism of flying. However, ere deciding that 

 this is so, numerous observations 0.1 different birds flying 

 and in different conditions of flight, during calms and 

 storms, and with and against the wind, must be taken. 

 Attempts were also made to photograph the bat, but its 

 small size, its flight during the dusk, and its capricious 

 method of flying made it a difficult subject; but some of 

 the experiments revealed interesting results. The angle 



of oscillation of its wings is very extended, especially from 

 below, when the two wings form two vertical planes 

 sensibly parallel. 



These extremely interesting researches of M. Marey are 

 only, as it were, in their infancy ; he intends pursuing 

 them much further, and his results will be looked for 

 with great interest by all those who study the subject ot 

 animal motion. 



DR. FRITZ MULLER ON SOME DIFFICULT 



CASES OF MIMICRY' 

 T N his original explanation of the cause of mimicry, 

 ■*■ Mr. Bates referred to the occurrence of many cases 

 in which species of different genera of Heliconidas re- 

 semble each other quite as closely as the mimicking 

 Leptalides and Papilios resemble species of Ithomia and 

 other Heliconoid butterflies. In these cases both the 

 imitating and t'.e imitated species are protected by dis- 

 tastefulness, and it was not therefore clear ho.v the one 

 could derive any benefit by resembling the other. Ac- 

 cordingly, Mr. Bates did not consider the^e to be true 

 cases o." mimicry, but to be due, either to ldcnti -al parallel 

 variations of externally similar form, or "to the similar 

 adaptation of all to the same local, probably inorganic, 

 conditions.'' 



Examples of this close resemblance of specie; of dif- 

 ferent genera of protected groups have now become very 

 numerous, and they often extend to three or more distinct 

 genera, some species of which imitate each other in most 

 parts of tropical America, each changing in a corresponding 

 manner as we pass from one district to another. 



In my Address to the Biological Section of the British 

 Association at Glasgow, in 1S76 (reprinted in "Tropical 

 Nature"), I connected these cases with a number of 

 others in which peculiarities of colour or of form appear 

 together in several groups not closely allied, but always 

 among those inhabiting the same locality and as fre- 

 quently among unpiotected (that is, eatable) as among 

 protected groups of butterflies ; and I concluded, gene- 

 rally, as Mr. Bates had done, that these curious pheno- 

 re due to "unknown local causes.'' 



Thus the matter rested, till, in 1879, Dr. Fritz Midler 

 published in /Cosmos a paper on " Ituna and Thyridia ; a 

 remarkable case of Mimicry in Butterflies"; and in 1881 

 a second paper, entitled " Remarkable cases ol acquired 

 resemblance among Butterflies," in which he gives a solu- 

 tion of the problem as really a case of mimicry. The first 

 of these papers was translated by Mr. R. Meldola, and 

 communicated to the Entomological Society of London 

 in May, 1S79, and the same gentleman has kindly fur- 

 nished me with a translation of the second paper (the 

 title of which is given below), which discusses the 

 whole question in great detail, and devotes mu;h spa e 

 to a criticism of my suggested " unknown local causes " as 

 a suffi:ient explanation of the phen imena. I may at 

 that I admit this criticism to be sound; and that 

 Dr. F. Midler's theory appears to me to afford a clue 

 (with some slight modifications) to most of the cases of 

 close individual resemblance of not-nearly-related species 

 of butterflies yet observed. I therefore wish to state, as 

 bricilv as possible, the exact nature of the explanation 

 now afforded us, and this is the more necessary because 

 I Jr. Midler's theory did not receive much support when 

 brought before the Entomological Society, nor did it then 

 satisf) Mr. Bates, the discoverer of the true meaning and 

 importance of the phenomena of mimicry as interpreted 

 by the doctrine of Natural Selection. 



The explanation depends on the assumption, that some 

 at least, if not all, young insectivorous birds learn by ex- 

 perience that the Heliconoid butterflies are distasteful, 

 and in so doing sacrifice a certain number of individuals 



' " Bemerkenswenhe FaUeerworbenerAehn1ichkeitl>eiSchmeuerlingen. M 

 Von Friti Mutter. (Separat-Abdrack aus •■ Kosmos," V. Jalirgang, 1881.) 



