LARVA—PUPA. 7 
and moisture. I have observed, also, that they are 
very often assorted according to age. It is sometimes 
very curious in my nests to see them arranged in 
groups according to size, so that they remind one of 
a school divided into five or six classes. 
As regards the length of life of the larve, Forel 
supposed! that those of Tapinoma matured the 
quickest, and were full-grown in about six or seven 
weeks. Some of Myrmica ruginodis, however, ob- 
served by me, turned into pupz in less than a month. 
In other cases the period is much longer. In certain 
species, Lasius flavus, for instance, some of the larvee 
live through the winter. 
When full grown they turn into pupz (PI. V. fig. 4), 
sometimes naked, sometimes covered with a silken 
cocoon, constituting the so-called ‘ant-eggs.’ We do 
not yet understand why some larve spin cocoons, while 
others remain naked. Asa 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. fusca) the pups 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 
tc see the older ants helping them to extricate them- 
' Les Fourmis de la Suisse, p 420. 
