226 



NATURE 



{June 27, 1878 



unnecessary to give here, as they will be accessible to 

 most readers who interest themselves on the subject of 

 binary stars. For the interval 1864-76, in which Mr. Hall 

 states he had not measures in his possession, the following 

 may be cited : — 



On the question of the brightness of the components Sir 

 John Herschel says : — " Individually their magnitudes 

 have been very differently estimated by other observers 

 from what I consider to be their coirect values. All 

 agree in assigning the first magnitude to the principal 

 star, or that which follows in R.A. (1834-37) ; but whereas 

 Lacaille, and after him Fallows, Johnson, Taylor, and 

 Messrs. Dunlop and Rumker estimate the preceding 

 star of the fourth magnitude, I have"never estimated its 

 magnitude as seen with the equatorial lower than 2-3, 

 and the mean of all the magnitudes assigned to it with 

 this instrument is 1-73, or if by a mean of eleven obser- 

 vations On the whole evidence afforded by my 



experience I am disposed to assign to it a magnitude 

 which may be deemed indifferently either a very low first 

 or a very high second." Sir John Herschel further con- 

 sidered that "it is not necessary to recur to the hypo- 

 thesis of variabiUty to account for this difference of esti- 

 mation," and gave his reasons for this opinion (" Cape 

 Observations," p. 300). 



BIOLOGICAL NOTES 



Decorative Colouring in Freshwater Fleas. 

 — There is something essentially comic in the notion of 

 a freshwater flea— a species of the entomostracous crus- 

 taceous Daphnoidae— becoming beautifully ornamented 

 with patches of scarlet and blue, for the purpose of 

 seducing the affections of the opposite sex. If a scarlet 

 coat is appreciated by the females of the very fleas of 

 this great family to which we all belong, we ought not to 

 be surprised at hereditary predispositions in favour of 

 this colour, and should conclude on this ground, as on 

 many others, that the civilian male Anthropini of western 

 Europe have taken a foolish and unnatural step, within the 

 last hundred years, in abandoning the use of brilliantly- 

 coloured clothing, and giving over the exceptional advan- 

 tages which it confers to soldiers and huntsmen. The 

 figures given by Prof. August Weismann, in the Zeitschr. 

 wiss. Zoologie (1878, Supplement i), show us the water- 

 fleas, Polyphemus and Latona, most gorgeously got up 

 an blue and scarlet. Goethe, though he never saw them, 

 foretold their appearance : — 

 ** Es war enimal ein Konig, der hatt' einen gros£en Floh, 



Den liebt' er gar nicht wenig, als wie seinen eignen Sohn, 

 *»»♦*» 



In Sammet und in Seide, war er nun angethan, 

 Hatte Bander auf den Kleide, hatt' auch ein Kreuz daran," 



&c., &c. 

 It is to the elaborate and ingenious studies of Prof. 

 Weismann on caterpillars — worthy to be placed by the 

 side of the most original of Mr. Darwin's own inves- 

 tigations — that we owe our knowledge of an exceedingly 

 important cause of animal coloration, namely, that which 

 is explained by the term "startling" or "terrifying" 

 colouration (Schreckfarben). Just as in various human 

 races the amorous of both sexes paint their faces and 

 adorn their bodies in order to attract one another, so 

 nature paints by sexual selection, and just as we dress our- 

 selves up in wigs and gowns and spectacles, or tattoo our 

 countenances in order to terrify evil-doers so (Prof. Weis- 

 mann shows) does nature paint masks with staring eyes 

 upon the feeble caterpillar's back in order that he may 

 enjoy the privileges so usually gained by the ass in the 



lion' s skin. Brilliant patches of colour occur only in a 

 few Daphnoidae (also in a few Phyllopoda), and after a 

 very detailed investigation as to the variations which 

 these patches of colour present in the different species, in 

 the two sexes, and at different seasons and at different 

 periods of growth, Prof. Weismann comes to the conclu- 

 sion that they must be regarded as a decoration acquired 

 by sexual selection which probably was first of all con- 

 fined to the male sex, but subsequently, in most cases, 

 became transmitted also to the other sex. Probably a 

 reciprocal and alternating sexual selection favoured this 

 transference to the female sex, the most brilliant females 

 being chosen by the few males existing at the commence- 

 ment of a sexual period, and the most brilliant males being 

 chosen by the relatively few females existing at the end of 

 such a period. The existence of these ** sexual periods" 

 is a well established feature in the life-history of Ento- 

 mostraca, alternating with parthenogenetic periods. From 

 the fact that neighbouring colonies of the same species 

 have a constantly differing arrangement of colour, it 

 appears probable that the development of these deco- 

 rative colour-patches took place after the isolation of the 

 colonies, that is to say subsequently to the glacial period 

 in northern Europe. The transference of the decorative 

 coloration originally developed only by the males, took 

 place in three directions— firstly to the other sex; 

 secondly to the not-yet sexually mature period of growth ; 

 and thirdly to the parthenogenetically produced gene- 

 rations. In the various species of Daphnoidae with 

 decorative coloration we find different degrees of com- 

 pleteness of the transference in these three different 

 directions. Only one species, viz., Latona, presents the 

 highest degree or complete transference of the coloration 

 to both sexes, all stages of growth and all generations of 

 the -annual cycle. Prof. Weismann concludes that the 

 Daphnoidae afford a further case in favour of the hypo- 

 thesis that secondary sexual characters can be converted 

 into general characteristics of the species, and that they 

 confirm Mr. Darwin's theory of the origin of the colour- 

 patterns of butterflies' wings. 



How Lepidoptera escape from their Cocoons.— 

 The mode in which butterflies and moths free them- 

 selves from their chrysalides has been a subject of some 

 controversy, but of very little recent observation. With 

 regard to the silkworm moth, Malpighi asserted that the 

 animal first wets the silk with a liquid calculated to 

 dissolve the gum that connects the threads, and then 

 employs its lengthened head to push them aside and 

 make an opening. Reaumur, however, maintained that 

 the threads of silk are not merely pushed aside, but are 

 actually severed, and believed that the eyes, which are the 

 only hard organs of the head, are the instruments by which 

 the threads are divided, their numerous minute facets 

 serving the purpose of a fine file. That the threads are 

 actually cut is the general view ; and the account of the 

 breeding of silkworms, published in the American Philo- 

 sophical Transactions, states that cocoons, out of which 

 the moth has escaped, cannot be wound. On the other 

 hand it is known to be a common practice with many 

 moths the chrysalis of which is very hard, to discharge, 

 immediately before issuing forth, a copious fluid from the 

 mouth by which the shell is so softened that they are 

 able to force their way through it. In an article in the 

 American Natnralist for June, Dr. A. S. Packard, after 

 reviewing our previous knowledge of the subject, gives 

 an account of some interesting observations of his own. 

 His attention being arrested by a rustling, cutting, and 

 tearing sound, issuing from a cocoon of the large green 

 swallow-tail silkworm moth, Actias luna, he discovered;, 

 on examination, a sharp black point moving to and fro, 

 and then another, until both points had cut a rough 

 irregular slit, through Avhich the shoulders pf the moth 

 could be seen vigorously moving from side to side. The 

 hole or slit was made in one or two minutes, and the 



