33 s ANTS. 



The gardens of . -I ptcrostnjina are provided with a special mycelial 

 envelope, but they are naked in all the other Attiine genera and sub- 

 genera. Mn'/lcnns and . Icroinynnc.v make a single large garden on 

 the floor of the single nest-chamber. Finally, in Atta s. str., the nest 

 attains huge dimensions and comprises a number of large chambers, 

 each with it- sessile fungus-garden resembling the single garden of 

 . Icroinynnc.v and Mcellerius. 



While thi> >eries of forms shows an interesting and significant 

 advance in the methods of raising fungi, it throws little light on the 

 origin of this complicated and extraordinary habit. Forel is inclined 

 to believe that the ancestral Attii lived, like the existing Apterostigma, 

 in rotten wood and gradually acquired the habit of cultivating on insect 

 excrement the fungi which they chanced to find in the moist galleries 

 of their nests. Yon Ihering surmises that the Attii are descended from 

 harvesting ants which transferred their appetite from the hard seeds 

 in their chambers to the delicate fungi that accidentally grew on these 

 stores. In this connection Santschi's observations on the seed-storing 

 Oxyopomyrmex, cited on p. 273, are very suggestive. Besides the 

 Attii there are also two other groups of fungus-growing insects, 

 the ambrosia beetles ( Scolytidse ), which cultivate fungus on their 

 excrement or on the walls of their burrows in the trunks of trees, 

 and a long series of paleotropical termites which raise fungi on 

 sponge-like masses of their excrement in large chambers like those 

 of Atta s. str. A study of these cases and of the female Atta while 

 she is establishing her colony, would seem to indicate that all fungus- 

 growing insects originally used their own excrement as a substratum 

 for their gardens and only later took to adding other substances (excre- 

 ment of other insects and pieces of leaves in the Attii, wood-shavings 

 in the ambrosia beetles). But how these various insects first came into 

 possession of the fungi which they now so assiduously cultivate and 

 transmit from generation to generation, we are unable to state, espe- 

 cially as our knowledge of these plants is still so rudimentary that we 

 cannot even say whether they are Ascomycetes or Basidiotnycetes, inde- 

 pendent species or merely permanently or temporarily modified phases 

 of certain well-known moulds or mushrooms. The study of the Attii 

 and other fungus-growing insects has only just begun, and further 

 advance in this fascinating subject will be more difficult for the mycolo- 

 gist than for the entomologist. The latter, however, will have to build 

 on the investigations of the former. 



