ants' nests. 493 



Til my opiniou, however, there is no doubt that the silk thread of 

 (Ecoph;/U<( and of the spinning species of Polyrkavhis, like the cement 

 of the other species of Polyrhachis, many of Cremastogaster and Doli- 

 choderus, Lasius fuliginosus, etc., is formed from the so-called mouth 

 saliva, ajid most probably from the secretion of the glands of the upper 

 jaw. The cells of these glands, at least in (Ecophylla, are large and 

 numerous. 



6.— SYMBIOSIS AND KINDRED RELATIONS BETWEEN ANTS AND PLANTS. 



By symbiosis, in the more restricted sense, is meant the mutual serv- 

 ices of two organisms living together, which, by a defensive alliance in 

 the struggle for existence, are so dependent upon each other tliat the 

 one can not thrive well without the other. The formation of si)ecial 

 morphological characteristics is usually combined with genuine sym- 

 biosis. There are, besides, all possible forms of im[»erfect symbiosis, 

 displaying transitions to parasitism, etc., above all, however, those in 

 which only one of the two organisms is really dependent upon the 

 other. For example, the small beetles Lomechusa and Atemeles can not 

 live without their ant host. On the other hand, the ant can exist very 

 w^ell without such guests, and merely eats the secretion from the hair 

 clusters of the beetles as a dainty (see Wasinann's elegant Observa- • 

 tious on the Biology of the Guests of the Ants). There are, however, 

 cases of still more imperfect, counterfeit symbiosis, where one organ- 

 ism entirely ignores the other, and, lastly, casual relations which are 

 erroneously regarded as symbiotic. 



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

 peculiar 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 Sxith. The ant genus Azteca 

 FoREL, which is related to Liometopum Mayr, contains several Ameri- 

 can 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 ov/n observations in 

 South lirazil, which substantially complete those of Miiller. 



Azteca instabilis lives only in the hollow trunks of certain species of 

 Cecropia, especially Cecropia adenopus, 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 adenopus and others, as soon as they have grown somewhat 

 large (1 year old), are always inhabited by Azteca instabilis. The fol- 

 lowing is now further ascertained : 



The pregnant females of Azteca instabilis seek out for themselves 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 



