146 



KNOWLEDGE. 



[August 1, 189S. 



Dr. Adler about fifteen years ago, and they have since 

 been confirmed by Lichtenstein and others. 



In brief, therefore, the entire life-history of this insect is 

 as follows. If we start with tbe currant galls, either on the 

 leaves or on tbe catkins, these produce at the end of Ma.y 

 the fly which is called Sjiatliffinster Imrcaniw. Both males 

 and females are produced, and the females, after mating, 

 pierce the oak leaves and deposit their eggs in the 

 punctures ; but from these punctures there do not proceed, 

 as might be expected, a further crop of currant galls, but, 

 on the contrary, a collection of spangles. These, after 

 maturing during the latter part of the summer, drop to 

 the ground in October, there swell and develop the 

 contained insect, which is now known as Xcitrotcnix 

 le7iticul-ii-is, and emerges in the following spring. This 

 spring crop of flies, however, are all of the same sort ; no 

 distinction of sex can be observed and no males are known. 

 They all produce eggs which they deposit in punctures on 

 the leaves or on the catkin stems, and from these 

 punctures are produced again, not spangles like those the 

 flies came from, but the currant galls of Spatlxiiastd' with 

 which we commenced the series. From these issue, as 

 before, male and female insects belonging to ^jKithi'nustt'r 

 liarraruiii, and the whole cycle is gone through again the 

 next year. Thus in the course of one year the same insect 

 appears in two successive phases, one of which has both 

 males and females and the other females alone, and 

 which make galls so utterly unlike in character as to have 

 been referred to two distinct genera. 



The phenomenon of parthenogenesis occurs in many 

 other species of gall-flies, but is not necessarily associated 

 with that of dimorphism, i.r., the occurrence of the same 

 insect in two distinct forms, and even in some cases, where 

 the males are known, their number bears an exceedingly 

 small proportion to that of the females. The marble gall 

 is an excellent illustration of the former peculiarity. 

 Mr. F. Smith, the zealous hymenoi^terist, obtained in the 

 year 1857 about a bushel and a half of Kollari galls from 

 Devonshire, as they were not then to be found in the 

 neighbourhood of London. At the beginning of April in 

 the following year flies began to emerge, and continued to 

 do so for two months. Altogether about twelve thousand 

 specimens were obtained, and all as they came out were 

 examined ; every one proved to be a female. About sixty 

 of the galls had been placed in separate boxes, and when 

 the flies issued from these they were conveyed to different 

 localities in the neighbourhood of London and placed on 

 low oaks and hedges. On revisiting these spots in August, 

 Mr. Smith found, in about two-thirds of the cases, galls 

 on the trees on which he had placed the flics, but on none 

 in the vicinity. These galls were again collected, and the 

 next year the flies bred from them ; these, again, proved to 

 be females. They were at once taken to other and isolated 

 spots and left on trees as before. Again, in the summer 

 galls were found in the same proportion as before. Thus 

 it was shown that the insect could breed from year to year 

 without males at all. 



The same observer obtained from one example of a root- 

 gall one thousand two hundred flies of Ajihilut/iri.r nidiris, 

 all of which proved to be females. Hartig, again, speaks 

 of having examined fifteen tliousaiid specimens of different 

 kinds of gall-llies without ever discovering a male. On 

 another occasion, from an enormous collection of twenty- 

 eight thousand galls of a species resembling the cherry 

 gall, he obtained between nine and ten thousand llies, all 

 of which were females. In fact, one may state generally, 

 that none of those species of oak gall-flies that arc single 

 brooded are known to possess a male at all. 

 (T<j he amtinuiil .) 



THE SUN AS A BRIGHT-LINE STAR. 



By !Miss A. M. Clerke, Authoress of " The Sijsti'm of the 



Stars" and "A Pojmlar History of Astronomi/ dtiriwi the 



Nineteenth Century," dr., dc. 



BY far the most remarkable pair of lines in the solar 

 spectrum are those known, since Fraunhofer 

 observed and named them, as "H" and "K.' 

 They lie high up in the violet — so high up, that 

 they can be much more easily photographed than 

 seen. Intense absorptive action is indicated by the depth 

 and extent of their central obscurity, which seems besides 

 as if veiled in diffusive shadow. Tliey are distinctive of 

 the metal calcium, which, however, emits them con- 

 si^cuously only under the stress of powerful electrical 

 excitement ; thus they may be provisionally termed "high 

 temperature lines." In the near neighbourhood of the sun 

 they are ubiquitous. The substance from which they 

 emanate rises to the summits of the loftiest prominences ; 

 it enters largely into the composition of the chromosphei'e ; 

 it shines even in '' white prominences" and facube. These 

 facts, although they have been securely established by the 

 recent investigations of Prof. Hale and M. Deslandres, do 

 not easily fit into the narrow framework of existing theories. 

 Yet of their profound importance to solar and stellar 

 physics there can be no doubt ; nor can they receive too 

 close or too careful consideration. 



There is evidence, to begin with, that the lines in 

 question (of wave-lengths 3968 and 3934 tenth-metres) 

 claiiu, in the sun, a three-fold origin. The wide dark 

 bands in the ordinary solar spectrum are produced by an 

 absorbing layer necessarily cooler than the photosphere, 

 and probably in its immediate neighbourhood. Calcium- 

 vapour seems here to be afl'ected very much as it is in the 

 core of the electric arc, where the H and K lines, just 

 traceable in a magnesium-flame, come out strong and 

 difl'use. Their centres are marked (as Prof. Hale has 

 noted) by thin, extra-black lines, possibly due to the 

 arresting action of the chromosphere. The chromosphere, 

 as the readers of Knowledge are well aware, completely 

 envelopes the solar globe with a tossing incandescent 

 ocean. The bright calcium-lines forming part of its 

 spectrum reach us clear, sharp, and undimmed from the 

 edge of the sun. Hence, evidently, the Fraunhofer 

 absorption takes place at a lower level than that at which 

 they are generated. Otherwise they would be hopelessly 

 cut oft' from transmission to outer space ; they would be 

 swallowed up by the superposed, powerfully absorbent 

 vapours. And the same reasoning applies, of course, to 

 tlie chromospheric rays of hydrogen. The H and K of the 

 chromosphere are of the same character with the lines 

 radiated by calcium during the passage of the electric 

 spark. They might, then, be supposed to indicate a higher 

 temperature than that corresponding to the dark bands in 

 the solar spectrum. But in our present inability to 

 discriminate between effects of simple heat and eft'ccts of 

 electrical agitation, no definitive judgment can be formed 

 upon this point. It appears certain, on the other hand, 

 that tbe chromosphere is not hotter than the photosphere; 

 for if it were, the calcium-lines of the ordinary solar 

 spectrum should be reversed all over the sun — that is to 

 say, a fine, brilliant ray would shine at the middle of each 

 dusky band. In fact, however, there are (as we have said) 

 fine, dark rays in these positions, most likely as tbe result 

 of a two-fold light-stoppage. P>iit with a chromosphere of 

 overweening radiative intensity we should get, instead of 

 double absorption, absorption plus emission. 



In faculio, on the contrary, reversals, which the 

 chromosphere is apparently incompetent to produce, do 



