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Show 342 MR. R. I. POCOCK OX THE [Apr. 21, the belief in the existence of a ‘ gossamer' spider which is supposed to be the cause of the fine threads which fall from the air and carpet the fields with silk at certain times of the year. It is now known that the 4 gossamer ' spider is a mythical species, and that species of the most diverse habits belonging to widely different families are responsible for the floating threads. The habit is practised alike, and, so far as is known, to an equal extent, by snare-spinning forms belonging to the Argiopidae and Theridiidae, by hunting-spiders like the Lycosidae and Attida?, or by sedentary species that lurk in flowers, like the Thomisidae. That this method of locomotion may considerably influence the distribution of spiders may be inferred from the fact that cobwebs thrown out in this way, and affording support to little spiders, have been found at the tops of our highest buildings, and have become entangled in the rigging of ships 200 miles from land. There are reasons for thinking, however, that the habit is for the most part restricted to plianerozoic diurnal species, namely, those that hunt their prey or spin their webs in the open; and that cryptozoic forms, that live in burrows or under stones or logs of wood, and that are for the most part nocturnal, do not indulge in it \ Clearly, therefore, these cryptozoic groups, in which the restrictions to dispersal are presumably the same as in other terrestrial animals which can neither fly nor swim to any distance, have more value for the establishment of geographical areas than those species with powers of dispersal analogous to flight. Owing to the relatively large size and great weight of the newly hatched young of the Mygalomorphae, coupled with the reduction in the number of spinning-appendages and the greater simplicity of the silk-glands, it seems probable that aerial sailing is not practised to any great extent by the members of this suborder2. Especially true will this be of the Aviculaiiidae, a family which contains the largest spiders known of this or any other epoch, with newly-born young rivalling or excelling in size the adults of many species of the Arachnomorphae. Consideration of these facts, coupled with the impossibility of dealing in detail, in one paper, with the distribution of all the genera of the Araneae, has led to the selection of the Mygalomorphae as the fittest group to illustrate the geographical distribution of Spiders in general. 1 Simon states that the Spider-fauna of the Sandwich Islands is composed wholly of species of the former category, with the exception of some few forms which appear to owe their presence in that Archipelago to human agency (£ Fauna Hawaiiensis/ Araneae, 1902). 2 The young of the only known British representative of this group, namely Atypns, one of the smallest types of Mygalomorphae, have been seen to scatter over small areas by this method of travelling (F. Knock, Tr. Ent. Soc. 1885). In this connection it is instructive to remark that Atypus has a wider distribution than any other known genus of the suborder, ranging from Ireland and Algeria to Japan and over the Eastern (? the Western) States of North America, that is to say across the Northern hemisphere from the eastern to the western shores of the Atlantic. |