LAEVA— PUPA. 7 



and moisture. I have observed, also, that they are 

 very often assorted according to age. It is sometimes 

 very cm^ious in my nests to see them arranged in 

 groups according to size, so that they remind one of 

 a school divided into iive or six classes. 



As regards the length of life of the larvse, Forel 

 supposed' that those of Tapmoma matured the 

 quickest, and were full-grown in about six or seven 

 weeks. Some of Myrraica ruginocUs, however, ob- 

 served by me, turned into pupae in less than a month. 

 In other cases the period is much longer. In certain 

 species, Lasius fiavus, for instance, some of the larvae 

 live through the winter. 



When full grown they turn into pupae (PL V. fig. 4), 

 sometimes naked, sometimes covered with a silken 

 cocoon, constituting the so-called ' ant-eggs.' We do 

 not yet understand why some larvae spin cocoons, while 

 others remain naked. As a general rule, the species 

 which have not a sting, spin a cocoon, while those which 

 have, are naked. Latreille was the first to observe that 

 in one species {F. fused) the pujDse sometimes spin a 

 cocoon, and sometimes remain naked. The reason for 

 this difference is still quite unknown. After remaining 

 some days in this state they emerge as perfect insects. 

 In many cases, however, they would perish in the 

 attempt, if they were not assisted ; and it is very pretty 

 to see the older ants helping them to extricate them- 



' Les Fourmis de la Suisse, p. 420. 



