June 2, 1881] 



NATURE 



1 17 



period runs through all the recorded obseri'ations of sun-spots 

 since the telescope came to be used. And furthermore it appears 

 that these eleven-yearly oscillations are not always of the same 

 magnitude ; sometimes they are large, and sometimes small. 

 They were probably small about the middle of last century, 

 becoming large towards the end of it ; they were again small 

 about the early part of the present century. They have recently 

 been large, and we may suspect that in future there will again be 

 a falling oft'. 



Besides exhibiting this complicated periodicity, sun-spots have 

 many other characteristics, the most prominent of which I will 

 now bring before you. Of the^e the most peculiar is a proper 

 motion of their own. If there were no sun-spots it would be 

 vei"y difficult to determine the elements of the sun's rotation. 

 Accordingly sun-spots have been used for this purpose ever since 

 the telescope was invented. They are carried by the solar 

 rotation from east to west across the visible disk of the sun in 

 about thirteen days, and hence we may conclude that the sun, 

 roughly speaUing, rotates round its axis in twice thirteen, or 

 twenty-six days. But Carrington found that spots move fastest 

 when nearest the solar equator, and slowest when nearest the 

 solar poles ; and in consequence of this proper motion of spots 

 there is an uncertainty as to the exact period of solar rotation. 

 Another point of interest is the distribution of spots over the 

 solar surface. There are never any at or near the sun's poles, 

 the zone in which they break out having its limits about 30° on 

 each side of the equator. It might be expected from this that 

 we should have a maximum of spots close to the equator, but 

 such is not the case. There are very few at the equator, the maxi- 

 mum number corresponding to a solar latitude of about 15" north 

 or south. We must not however conclude that spots invariably 

 exhibit a preference for this latitude, for Carrington has shown 

 that on certain occasions they appear by preference to seek a 

 higher latitude, widening out on each side of the solar equator 

 simultaneously, while at other times they prefer a lower latitude, 

 coming together towards the equator simultaneously on each side. 



Dr. SmyslofiT of the Wilna Observatory has likewise observed 

 a sort of hemispherical see-saw in the behaviour of spots. Some- 

 times they prefer the northern hemispliere of the sun — at other 

 times the southern ; but this observer is inclined to think that 

 if we pursue our researches for a length of time sufficiently great 

 we shall find an equal amount of spots in each hemisphere. 



I have thus endeavoured to bring before you the fact that 

 sun-spots exhibit curiously complicated laws of a roughly perio- 

 dical nature. Two questions arise from this discussion : the 

 one is of a theoretical nature, and has reference to the possible 

 causes of this behaviour ; while the other is of great practical 

 as well as of theoretical interest, and has reference to the eft'ect 

 which these strange solar phenomena produce upon the mag- 

 netism and meteorology of the earth and upon the general well- 

 being of the human race. 



To be continued. 



PROF. ALLMAN ON THE DEVELOPMENT 

 OF THE CTENOPHORA 

 T N accordance with his usual practice of making his anniver- 

 -'- sary address at the Linnean Society an exposition of recent 

 lirogress in certain departments of zoological research, the Presi- 

 dent on this occasion (24th May, 1881) selected as his subject the 

 advances which, during late years, had been made in oiu' know- 

 ledge of the development of the Ctenophora. 



He referred especially to the beautiful researches of Alexander 

 Agassiz, and to those of Fol, Kowalewsky, and most recently of 

 Chun. He pointed out the phenomenon to which he was the 

 first to call attention, that immediately after the earliest stages of 

 the egg cleavage a remarkable peculiarity shows itself, in the 

 fact that the continued cleavage is no longer uniform, but 

 takes place much more energetically in certain cleavage spheres 

 than in others, whereby the former are broken up into a multi- 

 tude of small cells, which gradually envelop the latter, thus 

 giving us at this early period of embryonic development the 

 foundation of the two germinal leaflets, ectoderm and endoderm. 

 He showed, how the body thus formed becomes excavated by an 

 internal cavity, which soon communicates by an orifice with the 

 exterior, thus pi'escnting, as shown especially by the researches 

 of Chun, the condition of a gastmla : how the gastmla-mouth 

 Ijecomes after\vai:ds closed by the continued extension over it of 

 the ectoderm ; how a new orifice, the permanent Ctenophore- 

 mouth, makes its appearance at the opposite hole, the ectoderm 



here becoming invaginated, so as to form the permanent stomach 

 which opens into the central cavity, which becomes the ' ' funnel " 

 from which spring all the vessels which are destined to distribute 

 the nutritive fluid through the body ; how, in the spot formerly 

 occupied by the gastrula-mouth, certain cells of the ectoderm 

 become diiferentiated, so as to form the rudimental nervoos 

 system ; and how the great vascular trunks are fonned by the 

 differentiation of portions of the endoderm, into which offsets 

 extend from the central cavity. 



Prof. Allman further referred to the facts connected with 

 the metamorphoses which the lar\-ce of the Ctenophora undergo 

 between the moment of leaving the egg and the attainment of 

 the mature form — facts for which we are mainly indeljted to the 

 researches of Alexander Agassiz and of Chun. He show'ed how 

 the lobed section of the Ctenophora, as proved by the investi- 

 gations of A. Agassiz on Bolina, and by those of Chun on 

 Eucharis, are at first quite destitute of the " lobes " which con- 

 stitute so characteristic a feature in the adult ; and how the 

 young Ctenophore has at this time all the characters of the more 

 simply constructed Cydipid^, Eucharis being also compressed 

 like a Merlcnsia in the direction of the stomach axis, while in 

 the adult the compression of the body is at right augles to this ; 

 how the lobes afterwards grow out laterally from the oral side of 

 the body ; how the meridional vessels at first ending in blind 

 extremities extend themselves into the rudimental lobes, and 

 there form the anastomoses and rich convolutions which become 

 so striking in the adult, the stomach vessels finally entering into 

 the anastomoses. 



He als5 referred to Chun's remarkable discovery of the 

 sexually-mature condition of the very early larva of Eucharis, 

 from which was reared a young brood which returned to the 

 larvK form from which it originated. 



Chun's observations on the metamorphoses of the Venus's 

 girdle (Cesium Veno'is) were also dwelt on. It was shown how 

 the young cestum had a nearly globular form, and possessed all 

 the essential features of the Cydipidae, so that notwithstanding 

 the extremely aberrant characters of the adult the young may be 

 taken as affording a type of the gastro-vascular system, w ith the 

 distriVjution of the vessels in the Ctenophora generally. The 

 gradual exten-ion of the Cydippe-like larva in the direction of 

 the funnel-jjlane changes it into the long, flattened, band-like 

 form of the adult, and brings aliout (with modifications in the 

 number and direction of the s\\ iumiing-plates, and the substitu- 

 tion of new tentacles to replace those of the larva which had 

 disappeared) the singularly alierrant course of the vessels charac- 

 teristic of the mature Venus's girdle. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Cambridge. — Mr. J. W. Clark is to be re-appointed Super- 

 intendent of the Museums of Comparative Anatomy and Zoolr-gy 

 for two years, at the end of which time the Council of the Senate 

 appear to anticipate that some fresh arrangements as to this office 

 may be made. 



Mr. W. Hillhouse, Assistant Curator of the Herbarium, will 

 give a course of lectures on Morphology and Systematic Botany 

 during July and August, suited to candidates for the Natural 

 Sciences Tripos. In connection with the course there will be 

 practical work in the Gardens and Botanical Laboratory ; and 

 a botanical excursion will be made, weather permitting, on 

 Wednesday in each week. 



Dublin. — The Professors of the Medical School in Trinity 

 College have, at the suggestion and with the sanction of the 

 Rev. Dr. Haughton, the senior lecturer of the College, intro- 

 duced into their summer courses of lectures, to a very large 

 extent, practical instruction, instead of the time-honoured and 

 now somewhat antiquated series of prelections. These summer 

 courses chiefly consist of Chemistry, Histology, Botany, Com- 

 parative Anatomy, and Operative Surgery. In the Chemistry, 

 instead of listening as formerly to an hour's lecture three times 

 each week, the students work in the laboratory under the 

 superintendence of Prof. Emerson Reynolds, F.R.S., for two 

 hours every alternate day, and on one day in each week attend a 

 demonstration by the Professor on the analysis of water, air, 

 and articles of food. In the Histology Prof. Purser gives 

 a lecture on one day in each week, at the close of which 

 illustrative preparations are shown in the laboratory. On 

 the other days the students are engaged on practical wofk 

 in the new physiological laboratory, where, as in the chemi- 



