20 KESE ARCHES OX FUNGI 



is geologically of considcniblc luitiqiiity, jind specimens have ofien 

 been preserved very perfectly in aniber.^ At the present day, in 

 the genus Mycetophila, a female " lays her eggs generally on the 

 under surface of the pileus, walking about over the surface first 

 to find a suitable place, then depositing the ova singly." ^ The 

 eggs of the Mycetophilida^ after being laid, quickly hatch and 

 develop into the well-known maggots. These feed on the stipe, 

 the pileus flesh, or even the gills ; and they often cause the 

 infested parts to become rapidly and prematurely putrescent. 



The gills of expanded fruit-bodies are frequently visited, not 

 only by Fungus Gnats, but also by Springtails (Collembola) and 

 Mites (Arachnida). As an instance, it may be mentioned that 

 on the under side of an unusually perfect fruit-body of FaxiUus 

 involutus, which had just opened, I observed members of all 

 these three groups present in some numbers. So far as my 

 experience goes, it seems to be rather the rule than the exception, 

 that at least some small animals are to be found on all large 

 fruit-bodies. When a pileus is disturbed, the Springtails and 

 Mites run rapidly over the gill surfaces, but the Gnats usually 

 fly away. Some fruit-bodies of Polyporun squaviosus, which were 

 growing on a log and had not yet become fully expanded, were 

 infested with small black Collembola. There were as many as 

 tifty to the square inch, and each one occupied a hymenial tube 

 which was just wide enough to hold it. The Springtails (genus 

 Achorutes), infesting the gills of Stropharia semiglohata and some 

 other species of Agaricinea?, Avcre found to contain spores in the 

 mid-gut. They are therefore parasites. It yet remains to be 

 investigated whether the hymenium, by means of its hairs, is 

 adapted in any way to suit its needs when visited by tiny animals; 

 or whether, on the contrary, Mites and Springtails, kc, are simply 

 to be re":arded as funj^^us fleas which have had no effect on the 

 phylogeny of their hosts. 



* Fossils have bi-eii found in tliu Ujiper Oolite beds in the Soutii of En<;land, 

 and also in the Solenhofen Slates. More than 280 species have been obtained 

 from the Tertiary in widely separated areas. Most of them were discovered in 

 the ambers of Europe and America, the rock specimens being few in comparison 

 (!7>?W.,p. 9.3). 



* Kred. V. Theobald, An Acrount of Britisth Flies (DijAera), vol. i., 189:2, p. 94. 



