ants' nests. 365 



towards him with all his might with his upper jaw. If the distance 

 was too great, from two to five ants chained themselves together 

 for this task, each grasping the body of one of the others, the first 

 holding one leaf with his mandibles, the last seizing the other 

 leaf with the claws of the tarsi. While the edges of the two 

 leaves were held as close together as possible, simply by these 

 chains of ants working side by side, with the application of all 

 their strength in the utmost tension, as if by india-rubber bands, 

 Aitken saw other ants zealously engaged in binding the edges of 

 the two leaves together with strong silk threads or ropes, which 

 they spun closer and closer together the nearer the leaves 

 approached each other. When a sufficient number of leaves had 

 been fastened together in this way by their edges, the whole was 

 rendered waterproof by a compact silk web, and was divided into 

 chambers and passages by a similar web. Aitken is a reliable and 

 accurate observer. This highly interesting observation of his is 

 entitled to full credit. Only one thing is wanting to it, to wit, the 

 information from what part of the body of the ant the silk thread 

 issues. This must likewise be observed. 



In my opinion, however, there is no doubt that the silk thread 

 of CEcophylla and of the spinning species of Folyrhachis, like the 

 cement of the other species of Folyrhachis, many of Cremasto- 

 gaster and Dolichoderiis^ Lasiiis fuligiiiosus, etc., is formed from the 

 so-called mouth saliva, and most probably from the secretion of 

 the glands of the upper jaw. The cells of these glands, at least 

 in CEcophylla, are large and numerous. 



6. — Symbiosis and Kindred Relations between Ants 



AND Plants. 



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

 services of two organisms living together, which, by a defensive 

 alliance in the struggle for existence, are so dependent upon each 

 other that the one cannot thrive well without the other. The 

 formation of special morphological characteristics is usually 

 combined with genuine symbiosis. There are, besides, all pos- 

 sible forms of imperfect symbiosis, displaying transitions to para-- 

 sitism, etc. ; above all, however, those in which only one of the 



