12 



KNOWLEDGE 



[NOVEMBEE 1, 1889. 



table to the animal kingdom, it is still in the steps by 

 which the adult form is reached that those changes are 

 revealed which almost entitle the barnacle to the reputa- 

 tion for facile metamorphosis with which our forefathers 

 credited it. The steps in question are 'besides the egg) the 

 two stages know respectively as the Xnupliux and Cyjin's 

 stages. Immediately on its escape from the egg the young 

 barnacle appears as an animal of microscopic size, active 

 and free-swimming, equipped with a broad shell or shield 

 on its back, and ha\ing three pairs of legs, a single eye, a 

 mouth and a forked tail. This is the XukjiUkis, and in out- 

 ward appearance the yomig creature exhibits at this stage 

 no single point of resemblance to the parent form. It feeds 

 and grows apace, and moults several times. It then enters 

 the next condition of its existence — the CijpriK stage. The 

 broad shield - shaped carapace becomes folded together, 

 somewhat after the pattern of a bivalved shell, and almost 

 encloses its owner. The foremost limbs are transformed 

 into a very peculiar pair of suctorial or adherent feelers, 

 and the two hinder pairs are cast off, their place being 

 taken by six pairs of powerful swimming-legs with bifid 

 extremities. A pair of compound eyes is another new 

 feature of this stage, and altogether the Ciniris, while still 

 quite distinct fi'om the adult barnacle, presents a very 

 different appearance from the Xaujilius. The mouth is want- 

 ing, or at least is fimctionless, being covered by an integu- 

 ment without aperture. Existence in this stage is therefore 

 necessarily short, and the L'ljpris soon fixes upon its futm-e 

 abode by attaching itself by its suctorial feelers to some 

 piece of drift-wood, pile, or rock. A kind of cement, which 

 it secretes by means of special glands, pours out roimd the 

 base of attachment and quickly hardens, gluing the ends of 

 the feelers firmly to the surface on which they rest. The 

 compound eyes are shortly afterwards moulted ; the body 

 straightens out, and the shell thus comes to stand almost 

 perpendicularly to the surface of attachment. Other 

 changes follow : the shape of the shell is modified, and the 

 position of the animal within alters in such a manner that 

 the under surface of its body is turned directly away fi-om 

 the point of attachment ; the integument covering the 

 mouth is cast off ; the legs cease all swimming ambulatory 

 functions, and soon become mere cirri sweeping the water 

 for prey ; the feelers are gradually covered with a fleshy 

 pulp, and, losing all trace of tlieir old form, are converted 

 into a single stalk of attachment ; the new parts of the 

 shell which are to form the valvular opening and other 

 protecting plates begin to form, and, for all practical pur- 

 poses, the barnacle, though still very minute, has attained 

 its adult form, future development being mainly in the 

 matter of size. 



The old legend involved a double change from friiit to 

 fish, and from fish to bird ; the new history also deals 

 with a double change, fi-om Xauijlinx to Ci/pris, and from 

 Ci/jjiis to barnacle. For one series of wonders another 

 has been substituted, and, if this is not sufficient to 

 restrain us from too hastily condemning our forefathers' 

 credulity, it will be well to remember how recently we 

 have arrived at the truth. Little more than fifty years 

 ago the position of the barnacle in the animal kingdom 

 was still completely vmsettled. Agreeing in most of its 

 outward characteristics with the mollusca, it was commonly 

 classed with them. The Xau])liii.'< and Cifprix were not 

 coimected with the j)arent form, but, if described at all, 

 were treated as distinct animals. In 1830 .J. Vaughan 

 Thompson's descrii^tion of his observations of their meta- 

 morphoses cast a new light on the subject, but the ques- 

 tion still remained somewhat open ground for naturalists, 

 and it was not imtil 18.51-.53 that Darwin, in his Munn- 

 (jniph of ilir ('in-ipciliii. definitely settled the barnacle's 



claim to be classed with the Crustacea, and established 

 beyond dispute the facts of its complicated and peculiar 

 life-history. 



Dr. Huggins has recently succeeded in obtaining a satisfactory 

 photograph of the spectrum of Saturn and its rings. He states that 

 the exact correspondence of the Frannhofer lines in the spectrum of 

 the sky (i.e. in the solar spectrum), and in the spectrum of the body 

 of the planet and its rings, is clearly shown. He is unable to detect 

 any lines, either bright or dark, which are not present in the solar 

 spectrum. He has obtained a similar result with the spectrum of 

 Uranus. 



A MEMOIR of Dr. Henry Draper has just been published by his 

 friend. Prof. G. F. Barker. 



Xottccs of Boolts. 



A Tf.ft-lUiiik lit (ioii'nil Axtronomij. By Chas. A. Young, 

 Ph.D., LL.D., Professor of Astronomy in the College of 

 New .Jersey. (Boston, U.S.A., and London: Ginn & Co.) 

 — A second edition of this valuable book has been called 

 for within six months of the publication of the iJrst edition. 

 To call it a text-book is almost misleading. It is rather an 

 encyclopoedia than a text-book, for it contains information 

 on a very wde range of subjects connected with physical, 

 as well as general, astronomy, arranged m numbered para- 

 graphs imder well-chosen headlines, and the whole is 

 referred to by a copious index. Many of these paragraphs 

 are admirable specimens of condensation, but the art of 

 abbre^^ation has not been carried too far ; the explanations 

 remain lucid, and adapted, as Prof. Yoimg desires they 

 should be, to the comprehension of any " Uberally educated 

 person"; they require, in fact, a knowledge of elementary 

 algebra, geometry, and trigonometry. It is refi'eshing to 

 find such a liberal use of the term "liberally educated." 

 On this side of the Atlantic the phrase " a liberal educa- 

 tion," as well as the terms "scholar" and "a man of 

 scholarship," only convey to most minds an idea of 

 classical erudition ; but we are, perhaps, a little in advance 

 of the language we use. Prof. Young's book ought cer- 

 tainly to be imderstood by an intelligent school-boy. It 

 would be impossible to treat so large a subject without 

 making some statements which might be criticised, and 

 without laying oneself open to the charge of ha\-Lag dealt 

 with many subjects which are of less importance than 

 others that have been omitted. 



Prof. Y'oung has treated his own especial subject, the 

 sun, very meagrely. The polarised condition of the light 

 of the corona is not referred to. The remarkable con- 

 nection between the general form of the corona and the 

 development of smi spots is not noticed, nor is the 

 remarkable bending together of coronal structures into 

 groups referred to. Only one picture of a corona is given, 

 and that is wrongly oriented. It has its north pole where 

 its eastern equatorial region ought to be. Curiously, the 

 same mistake is made with regard to the same picture in 

 the last edition of Cliaiiiheix Handbook of Astronomi/, p. 48G. 

 Probably both mistakes are due to a mistaken orientation 

 of a woodcut in an early number of Kxo^-ledge, which was 

 one of the first pictures of a photograph of the corona taken 

 during the eclipse of IHS'2 that was published. According 

 to it, the comet " Tewfic," which was seen near to the sun 

 during the Egyptian eclipse, was moving in an easterly 

 direction, instead of northward, nearly at right angles to 

 the ecliptic. 



Prof. Y'oimg estimates the growth of the earth, due to 



