1899] DISTRIB UTION OF THE ARA CHNIDA 2 1 5 



45° N., where, according to Mr. Buchan's charts, the mean temperature 

 of July is the same as that of South Europe, but that of January is 

 lower than that of the north of Scotland. So, too, in the case of the 

 tailless Pedipalpi, although they only pass a short distance to the north 

 of the Tropic of Cancer, yet they have been met with in Patagonia as 

 far to the south as latitude 50°, where the mean annual temperature is 

 only about 40° Fahrenheit, being about 55° in midsummer (January) 

 and 34° in winter (July). 



Moreover, the structural differences that obtain between the species 

 capable of withstanding for some months of every year the lowness of 

 temperature expressed or implied in the above statements, and the 

 species that inhabit tropical or, at all events, very much warmer climes, 

 are often only of specific importance. For example, the Manchurian 

 Pedipalp (belonging to the Thelyphonidae) is closely related to one 

 that occurs at Hong Kong, to the south of the northern tropic ; the 

 Patagonian tailless Pedipalp is congeneric with a form that is found in 

 equatorial East Africa ; the Galeodcs of the Russian steppes is a near 

 ally of a species that flourishes in the perennial heat of the deserts of 

 South Arabia and Somaliland ; and the Alpine scorpion is similarly 

 related to forms that exist in South Italy and Algeria. 



So, too, with regard to moisture. Although, broadly speaking, it is 

 true that desert forms are not met with in forest-covered areas, never- 

 theless genera of Solifugae, which abound in the arid plains of Arabia 

 and North Africa, have representative species in parts of West Africa 

 and India, where vegetation is luxuriant. Congeneric species of 

 Amblypygous Pedipalpi occur in deforested tracts of South Arabia, and 

 in Malabar and Ceylon, where the physical conditions are very 

 different, and a species that has been found in caves in the Philippine 

 Islands has been collected by Mr. Oates beneath stones on the sea- 

 shore in the Andamans. Nearly allied species of Butheolus (scorpions) 

 are met with in Sind, with an annual rainfall of about four inches, and 

 at a place in Satara in the Dekhan, where the average fall is about 

 thirty inches. And lastly, Professor Wood Mason's statement that 

 species of whip-scorpions were only discovered in Assam during the 

 heaviest rains and soon died^ when removed from their humid 

 surroundings, should be compared with that of M. Schwarz to the effect 

 that the Floridan species frequents dry and sandy spots. 



From these data it is evident that the Arachnida in question have 

 very considerable powers of adaptation to varied physical conditions. 

 Consequently their absence from certain areas of the earth's surface 

 must not be too hastily explained away on the plea of unsuitability of 

 environment. 



Unfortunately our knowledge of the fossil forms of these animals 

 is extremely scanty. Of the past history of the Solpugas we know 

 absolutely nothing. Pedipalpi, referable both to the Uropygi and 

 Amblypygi, have, however, been discovered in Carboniferous strata. 



