366 ants' nests. 



two organisms is really dependent upon the other. For example, 

 the small beetles Lomechusa and Atemeles cannot live without 

 their ant-host. On the other hand, the ant can exist very well 

 without such guests, and merely eats the secretion from the hair 

 clusters of the beetles as a dainty (see Wasmann's elegant Obser- 

 vations on the Biology of the Guests of the Ants). There are, 

 however, cases of still more imperfect, counterfeit symbiosis, where 

 one organism entirely ignores the other, and, lastly, casual rela- 

 tions which are erroneously regarded as symbiotic. 



The relations of certain ants to certain plants give rise to very 

 pecuUar forms of nests, of which we will speak briefly. 



(a) Genuine symbiosis. — Dr. Fritz Miiller, of Blumenau, South 

 Brazil, has discovered the real relation of the Cecropia trees (the 

 imbauba of the Brazilians') to Azteca instabilis. Smith. The ant 

 genus, Azteca, Forel, which is related to Lioffietopmn, Mayr, con- 

 tains several American species, but the biology of Azteca instabilis 

 only is known. Prof. A. F. W. Schimper {The Varying Relations 

 between Plants and Ants., Jena, 1888) has given us in his excellent 

 work his own observations in South Brazil, which substantially 

 complete those of Miiller. 



Azteca ittstabilis lives only in the hollow trunks of certain 

 species of Cecropia, especially Cecropia adefiopus, which trunks are 

 divided into chambers by transverse compartments ; but Schimper 

 has discovered a species of Cecropia on the Corcovado, which 

 never contains ants, while Cecropia adenopiis and others, as soon as 

 they have grown somewhat large (1 year old), are always inhabited 

 by Azteca instabilis. The following is now further ascertained : — 



The pregnant females of Azteca instabilis seek out for them- 

 selves a certain very thin and soft spot in the trunk of the 

 Cecropia, which always has the same situation in every internode, 

 bore into it, and thus get into the hollow, where they deposit their 

 brood, if they are not attacked by parasites (ichneumon flies). 

 The opening then closes, but is subsequently opened again by the 

 worker ants. This thinned spot is an adaptation of the plant to 

 the ant ; it does not occur in the Cecropia, which is free from ants 

 (that is to say, the corresponding bud depression is not changed 

 in texture and is not atrophied). On the underside of the stem of 

 the leaf of Cecropia adenopus and others is a peculiar hair cushion, 



