442 WILLIAM M. MANN 



times by the ant before the slit on the tenth segment opens and 

 the papilla which bears the drop of liquid is thrust out. The 

 ant laps this up, while it is stroking the larva with its antennae. 

 L. piasus emits a drop of the liquid about once every fifteen 

 minutes. The stroking of the larva by the ants acts as a stimulus 

 which causes either the ejection of the liquid or, in case the 

 organs aie not in a condition to exude, the eversion of the re- 

 pellant organs of the eleventh segment. 



Pi^ron (29) gives a general survey of the observations and 

 experiments by various investigators on the problem of orien- 

 tation in ants. As far back as 1745, when Bonnet published 

 on the subject, it has been known that the sense of smell plays 

 an important role in guiding the ant back to its nest. Huber, 

 Forel, Bethe and others have confirmed this, till there is no 

 doubt as to its truth, and Santschi has recently shown that 

 certain species by means of touching the ground with the tip 

 of the gaster actually make an odoriferous "intentional" trail. 

 The differences in this trail, which naturally varies in intensity 

 close to and remote from the nest, are appreciated by the "topo- 

 chemic sense" (Forel) and are therefore valuable in orienting 

 the ho me -going ant. Odor plays a more important role with 

 those ants which have a collective trail, except in some 

 forms, like the wandering Ecitons and the slave-making Poly 

 ergus, the armies, of which do not return directly by the out- 

 going trail. In the case of isolated foraging ants, in the environs 

 of the nest, it is probable that sight, smell and touch are all 

 employed, different forms of ants varying in the degree in which 

 these various senses are used. Thus Lasius is considered by 

 Pieion to be an olf active type, Formica and Camponotus visual 

 types and Messor a muscular type. Orientation at a distance 

 from the nest opening has been explained in a number of ways, 

 and it is probable that the muscular memory and the influence 

 of the light are both important elements, though neither fully 

 explains the problem. The ant does not exactly retrace its 

 steps and probably makes more movements on the out-going 

 than on the returning trip, which may cause considerable error 

 in locating the nest again, while the impression given by the 

 light is obviously received only by diurnal species. Pi^ron 

 points out that the agricultural ants — Messor — of Erytrea stop 



