October 1, 1894.] 



KNOWLEDGE 



235 



Pleiades cluster we have a range of apparent brightness 

 which corresponds to at least twelve and a half magnitudes, 

 that is, the brighter stars of the cluster give one hundred 

 thousand times as much light as the smaller stars which, 

 it will hardly be doubted, are at the same distance from 

 us as the large stars of the cluster, and in the case of the 

 cluster about a Cruois there is probably a range of at least 

 fifteen magnitudes, which corresponds to a light ratio of 

 one to a million. 



If we adopt Mr. Gore's theory with regard to the great 

 distance and size of these star clusters, we are carried back 

 to the old theory, that clusters and nebulas are distant 

 galaxies, outside and unconnected with the Milky Way 

 system ; an assumption which has very generally been 

 rejected since the publication of Herbert Spencer's paper 

 on the " Nebular Hypothesis " in the Weatviitister Berieir 

 for July, 1858, in which he showed that the general distri- 

 bution of nebuliB and clusters corresponded with and was 

 complementary to the general distribution of luminous 

 stars, proving that the nebuls and clusters were membprs 

 of the galactic system — a fact which was brought out 

 still more clearly in 1869 by Mr. Proctor's papers and 

 charts illustrating the distribution of nebula and clusters, 

 and which is now still further enforced by the beautiful 

 charts of Mr. Sydney Waters, published in the last number 

 of the Monthly Xotices. 



Assuming, then, that the star clusters are at the same 

 distance ft-om us as the Milky Way and the large stars 

 associated with it, we must either believe that the first 

 magnitude stars connected with the Milky Way are millions 

 of times larger than our sun or that the small stars of the 

 clusters are much smaller than the sun, and in some cases 

 probably smaller than the earth, if they compare in bright- 

 ness with our sun. — A. C. Ranyakd.] 



ON THE INHABITANTS OF SOME COMMON 

 GALLS. 



By the Rev. Alex. S. Wilson, M.A., B.Sc. 



ON certain plants swellings, excrescences, and defor- 

 mities of various kinds occur, caused by the action 

 of insects. The oak-galls imported in quantities 

 from the Levant, and largely used in the manu- 

 facture of ink, are of this nature. Gall-making 

 insects show a marked preference for the oak, but some 

 species select the willow, poplar, and other trees, while 

 others confine themselves to various species of shrubby or 

 herbaceous plants. The study of galls opens up a sin- 

 gularly interesting chapter of natural history. To the 

 entomologist they oli'er an inviting field for original research; 

 for the botanist they have at least a pathological signifi- 

 cance ; some knowledge of them is of practical use to 

 farmer and gardener ; while the attractive appearance of 

 some kinds is fitted to excite the curiosity of every obser- 

 vant lover of Nature. 



Besides the insect which makes it, a gall is often tenanted 

 by other species, termed inquiUnes, from the Latin inqui- 

 linux, meaning a lodger. Of this fact the writer had 

 evidence afibrded lately by finding on the common ger- 

 mander speedwell a gall, which, when opened, was found 

 to contain four orange-coloured larvre, along with three 

 white ones which apparently belonged to another species 

 altogether. The cuckoo's egg in the hedge-sparrow's nest 

 at once rose before the mind, and it was difficult to resist 

 the conclusion that we had before us evidence of a similar 

 habit on the part of insects. To place the matter beyond 

 doubt, it would have been necessary to rear the perfect 

 insects from the gall. Unfortunately, an attempt to do so 

 proved unsuccessful. On a former occasion, fi'om an ab- 



normally thickened twig of the pine which was placed 

 under a glass shade we obtained after some days a whole 

 swarm of midges. Some such method is followed when it 

 is desired to rear the insects from the galls ; the shoot or 

 leaf which bears the galls is placed in water and covered 

 with muslin, or, better, in a wide-mouthed bottle, having 

 damp sand in the bottom. For this purpose the more 

 advanced galls must be selected. It is a common ex- 

 perience in experiments of this kind that instead of a 

 single species difl'erent kinds of fly emerge from the same 

 gall, and it is not always easy to determine which is the 

 original gall-maker. In this way it has been ascertained 

 that the gaUs of the Cynipidfe are often inhabited by other 

 species of Cynips, of Synergus, Amblynotus, and Synophrus. 

 On one of the willows a gall which resembles a pine- 

 cone grows ; it is made by a large species of Cecidomyia, 

 which inhabits the centre, and in the outer part numerous 

 smaller species of Cecidomyia take up their abode. 

 Certain saw-flies are inquilinous in the galls of the 

 gall-gnats, and certain of the latter return the compli- 

 ment. In many cases the iuquiline causes the death 

 of the original inhabitant, but in other instances a 

 iiiodtis vivfiiili seems to be arranged, landlord and lodger 

 contriving to exist together in harmony, sharing the sub- 

 stance of the gall for food. Certain kinds of beetle have 

 also been found in galls, for whose presence it is not easy 

 to account, seeing they are not gall-feeders. Both the 

 gall-maker and its guests are liable to the attacks of 

 parasitic insects, especially of ichneumon flies ; these 

 deposit their eggs in the larv* within the gall. For this 

 reason it often happens that from a gall one may fail to 

 obtain any perfect insects except the parasitic species. 

 Other hymenopterous parasites are the Proctotrypidas and 

 Chalcidie ; the larva of one of the latter preys on the 

 larvae of Cynips glutincsa, and its lodger, Syneryus facintus. 

 It is otherwise with the Braconidae and Ichneumonidse 

 occurring in the oak-apple ; these are believed to be 

 parasitic, not on the owner of the gall, but on the 

 inquilinous Tortricidfe. 



As the guests may belong to difl:erent species, and as not 

 only the gall-maker but each of the lodgers may have 

 their own specific parasites, we may have an extraordinary 

 variety of insects inhabiting the same gall. From one of 

 the wUlow-gaUs Mr. B. Walsh obtained sixteen difl'erent 

 insects, preyed upon by eight others, twenty-four in all, 

 representing eight orders — quite a respectable entomo- 

 logical collection. 



The treasures of the hive are liable to be appropriated 

 in a similar way by intruders, such as the fly Volucella, 

 which eft'ects an entrance more easily on account of its 

 deceptive resemblance to a bee, but the honey gatherers 

 would seem to have much less cause for complaint on this 

 score than have the makers of the galls. 



Dr. Adler arranges the inhabitants of galls under three 

 heads— gall-makers, inquiUnes, guest flies or cuckoo flies 

 and parasites. He also mentions commensals, under 

 which may be included those beetles, already referred to, 

 which do not feed on the galls, and also the larvte of certain 

 moths whicli Mr. P. Cameron describes as attaching them- 

 selves to the exterior of galls and feeding on them, but 

 without interfering with the occupants. The larviB of the 

 inquiline usually develop more rapidly than do those of 

 the gall-maker, and a saving of time may be one of the 

 advantages which the inquilinous habit secures. Such at 

 least appears to be the advantage in the case of the cuckoo ; 

 for the remarkable instinct of this bird, there can be little 

 doubt, has reference to the shortness of its stay in this 

 country. The young cuckoo, a few days after it is hatched, 

 is said to eject the young hedge-sparrows from the nest, and 



