34 BRITISH ANTS. 



The pupal skin, which closely covers the body and limbs, and 

 which of course is the only covering of naked pupae, is also care- 

 fully stripped off by the workers, though ants may free themselves 

 from it. If it is not thoroughly removed, it may produce cripples, 

 especially in the winged sexes. I have frequently saved young 

 callows, which had not been properly attended to by their mother, 

 or foster-mothers, in my nests, by carefully removing the remains 

 of the pupal-skin with a wet paint-brush. 



The duration of the pupal period is shorter than that of the 

 larval one, and may occupy two or three weeks. 



The pupae are kept in drier parts of the nest than are the eggs 

 or larvae, and some species of ants build special incubators of 

 earth, or vegetable detritus, etc., to accelerate their development. 

 Ants kept in plaster -nests in a warm room will pile up their pupae 

 in the chamber nearest to the fire, and watch over them for some 

 time it is very amusing to observe a worker suddenly seize a 

 pupa and hurry off with it, as fast as she can, back to the cooler 

 chambers, as if it was a joint before the fire, and was just cooked 

 to a turn. 



Temperature undoubtedly influences both the period for egg- 

 laying and the time required for development of the brood. 



In my observation-nests kept in a hot room the queens of some 

 ants, which in nature would not lay before the spring, have com- 

 menced to do so as early as December. 



The eggs, larvae and pupae of all British ants which I have been 

 able to find will be briefly described below under their respective 

 species or genera. 



Polymorphism. Ants vary exceedingly both in habits and struc- 

 ture, it being almost impossible to lay down rules on any points 

 concerning them, to which exceptions cannot be found. In the 

 following points and many others might be mentioned ants vary, 

 not only in different genera and species, but often in the same species 

 itself : the time for the appearance of the sexes, and for the marriage 

 flight ; whether the males and females are winged or wingless ; 

 whether the former are more abundant than the latter, and whether 

 they are both present at the same time, or in the same nest ; whether 

 the ocelli are present or absent in the wingless forms (worker, 

 male or female) ; whether the larvae occur in the summer or winter 

 or both ; whether the pupae are naked, or enclosed in cocoons ; 

 how the colony is founded ; in what situations, and under what 

 circumstances the nests will be built, etc. etc. 



These variations however are not what is understood by poly- 

 morphism in ants. 



Polymorphism is possessed by those species in which the sexes 

 one or both of them occur in two or more forms ; these forms 

 being more or less regularly produced in certain generations, or in 

 each successive generation, which are sprung from the same parents. 



