January, 1911. 



KNOWLEDGE. 



29 



THE AUTUMN OF 1910.— For Meteorological purposes 

 the Autumn is taken as the three months, September. October, 

 November, and of the thirteen weeks. September 4th to 

 December 3rd, 1910, in England S.E., four weeks have been 

 unusually warm, eight weeks unusually cold and only one 

 week about normal. During the same period five weeks have 

 been classed as weeks of heavy rainfall, four as weeks of light 

 rainfall and four weeks as normal. The sunshine in five 

 weeks has been abundant, in six weeks scanty, and in two 

 weeks normal. 



THE S.E. TRADES AND RAINEALL.- 

 Dr. W. N. Shaw called attention to 

 a remarkable apparent relation between 

 the strength of the S.E. Trades, as 

 recorded at St. Helena, and the 

 rainfall in England, and the suggestion 

 then made has stimulated research 

 in various directions. In a paper just 

 published in the Quarterly Journal 

 of the Royal Meteorological Society. 

 Mr. J. I. Craig, of the Egyptian 

 Weather Service, expresses the opinion 

 that .a distinct connexion has been 

 traced between the winds at St. Helena 

 and the Rainfall in Northern Africa. 

 If this opinion is confirmed on further 

 investigation, it will be of great 

 practical importance ; for the Nile 

 flood depends on the rainfall in 

 Abyssinia and the adjacent regions, 

 and any reliable prognostication of 

 the probable Nile' flood should be 

 of immense advantage to Egypt. 



SNOW IN JOHANNESBURG.— 

 Mr. H. E. Wood, in a paper in the 

 South African Journal of Science 

 for September, says: " On the morning 

 of August 17th, 1910. the town of 

 Johannesburg, for the first time in 

 its history, was covered with snow 

 to a depth of several inches. To 

 many of its inhabitants, particularly 

 the younger generation, the sight of 

 snow was quite new. The result 

 the unusual event was 

 bv a general holidav in 



-Some vears ago 



was that 

 celebrated 

 the town." 



Figure 1. 



Thyrcosthcniiis bioi'atus, male. Front view 



of head showing cephalic prominences and 



extraordinary arrangement of eves. 



MICROSCOPY. 



By A. W. Sheppard, F.R.M.S.. 

 with the assistance of the following niicroscopists : 



Arthur C. Bankield. 

 James Burton. 



The Rev. E. \V. Bowell, M.A. 

 Charles H. Caffvn. 



Arthur Earland, F.R..\I.S. 

 Richard T. Lewis, F.R.M.S. 

 Chas. F. Rousselet, F.R. M..S. 

 D. J. ScouRFiELD, F.Z..S., F.R..M.H. 



C. D. Soar, F.R.M.S. 



A MVRMECOPHILOUS SPIDER iThyreostheniiis 

 hiovatus). — A good deal of interest always attaches to the 

 heterogeneous assemblage of creatures which for some reason 

 or other are permitted to spend their existence, or part of their 

 existence, in company with xarious species of ants, and a few 

 remarks, therefore, concerning a small spider somewhat 

 notorious in this respect, may not be altogether out of place 

 here. 



Many species of spider have been, at one time or another, 

 recorded as having been found in ants' nests, but. upon careful 

 investigation of their claims, only three of our British spiders 

 can be considered to be really myrmecophilous. namely. 

 Tetrilus arietinus, Evansia merens, and Thyreosthenius 

 biovatus. It is easy to comprehend how mistakes are liable 



to arise in this matter. Manj' small souicrs are found under 



stones, or amongst the vegetation grov^-irj.; against the sides of 



pieces of rock ; and when the protecting I 'dy is turned over 



it is the simplest thing in the world for the . oider to drop into 



a nest of ants should there be one undernt h Spiders, too, 



are often captured apparently wandering upc the surface of 



the nest of the wood-ant {Formica rufa); ;'it it will be 



noticed that it is usually in the case where a la^ . : nest has 



been disturbed, and the surviving ants have coiu^lructed a 



comparatively small nest upon the summit of the damaged one, 



leaving a bulk of uninhabited material upon which intrudiiig 



creatures may venture with some amount of safety. In several 



such instances in a wood in the North 



of London I have found large numbers 



of a small spider (Tiso vagans) 



actually living amongst the debris of 



,^ - the nest, but in no case were the 



spiders found in the central portion 



where the nmch-persecuted ants still 



held their own. It would, however, 



have been extremely easy to have 



fallen into error, especially as the nests 



were of a lighter and more friable 



character than is usually the case, and 



it was consequenth' by no means easy 



to decide where the inhabited portion 



ended and the debris commenced. 



Thyreosthenius hiovatus is, in the 

 male sex, a most grotesque and striking 

 creature; but, on account of its small 

 size, its peculiarities are hardly visible 

 even to highly trained eyes, unless a 

 lens be employed. The female, on 

 the other hand, is a most ordinary 

 looking creature, and indistinguishable, 

 except by careful microscopical exam- 

 ination, from quite a number of allied 

 spiders. Both sexes, even when fully 

 developed, are of a somewhat pale 

 colour, and convey the impression of 

 immaturity. 



The only species of ant with which 

 they associate appears to be the wood- 

 ant {Formica rufa). So far as I am 

 aware the reason for their presence in 

 the nest is quite a mystery. It seems 

 pretty clear that they do not feed upon 

 the ants, which are in size and fighting 

 capabilities vastly superior to them ; 

 and it seems unreasonable to suppose that they destroy the 

 various small creatures which the ants harbour as sca\engers 

 or pets. Still, the so-called intelligence of the ant has been 

 enormously exaggerated, and it is not beyond the range of 

 possibility that the spider may be fooling its hosts, and 

 perchance making meals at the expense of their offspring 

 when the nurse's back is tiu'ned. When the nest is disturbed 

 the spiders do not feign death, but generally extricate them- 

 selves from the debris and are quite easily seen. Isolated 

 specimens are occasionally found wandering at some 

 considerable distance from any nest, but, so far as I have 

 been able to ascertain, not in an\' district where the wood- 

 ant does not occur. As a rule the males appear to be 

 considerably rarer than the females, but it is quite possible 

 that, as in the case of many other spiders, the life of the 

 adult male is a short one. 



In some of the very restricted pine areas of south-east 

 Sussex, during the early part of October, specimens of 

 Thyreosthenius are sometimes to be found in the small 

 newly-formed nests which are plentiful where larger nests 

 have been destroyed bv the gatherers of " ants' eggs." These 

 nests vary considerabK' in character, some being ver\- rich in 

 pupae and others being almost devoid of anv but adult ants. 

 It is a curious fact that I have never found a single spider in 

 a nest where pupae were very numerous. At the season 

 mentioned, namely, early October, the majority of the captures 

 were males, and almost all of these, as well as the females, 



