THE CANADIAN ENTOMOLOGIST 79 



In addition to the conspicuous organs we have been discussing, the Col- 

 lembola display several minor structures that no doubt are sense organs of 

 some kind, but what their precise functions are, and indeed what senses the 

 insects really possess, we can only guess. Many species seem to get along quite 

 well without sight, and the eyes of those endowed with vision are very simple 

 constructions compared with the enormous compound eyes of some of the flying 

 insects. The sense of touch— the most primitive of all the senses, and com- 

 mon to every manifestation of life — is doubtless served by the numerous strange 

 "hairs" that cover the insects' bodies as well as by the antennae. The very neces- 

 sary sense of taste it is reasonable to suppose is situated in the mouth. And possibly 

 the closely-allied sense of smell has its seat in the curious depressions each with 

 a "peg" in the centre that sometimes indent the sides of the antennae, or in the 

 remarkable buds and tubercles often seen on the same organs. But it is hard 

 to divine the use of the strange bladder-like sac that Achorutes armatus Nic. 

 can evert from between its last two antennal segments. Equally mysterious 

 are the "post-antennal organs," those rosettes of scales situated on the head 

 between the base of the antennae and the eyes in many species. They may be 

 auditory, but, of course, we have no evidence that the insects can hear at all. 

 Another peculiar feature of certain species are the two or three sharp, curved 

 spines that grow out of the last abdominal segment. But whatever use these 

 "anal horns" are to the animal, at least they justify their existence to the puzzled 

 entomologist by helping him in the often difficult task of determining the species. 



As the systematic observation of such minute insects in their habitat is 

 practically impossible, and as it is very difficult to keep them in captivity under 

 natural conditions, the details of their life-history are not well known. 



The CoIIembola pass through no larval stage, and undergo no metamorphosis 

 whatever. The white or yellow spherical eggs, about one-eighth of a milli- 

 meter in diameter, are generally quite smooth, although- Nicolet figures some 

 hairy- ones. They are laid singly or in masses like bunches of grapes under bark, 

 among dead leaves and in many other damp situations. The masses often 

 contain from 50 to 100 eggs, and bulk much larger than the body of the insect, 

 but are usually all stuck together with every appearance of being the product 

 of one female. Oviposition apparently takes place only in the dark. Several 

 species lay eggs freely in captivity, but I have never been able to observe the 

 operation; and an English writer says that in 50 years' study of the insects he 

 has never succeeded in seeing how the eggs are laid. Until some one discovers 

 how to circumvent this coyness of the mother springtail, we shall not know 

 whether, despite appearances, more than one female contributes to the egg 

 cluster, or whether we must accept the decidedly improbable suggestion that the 

 eggs increase in size after laying. 



Incubation at room temperature takes from 10 to 35 days, according to 

 the species. The large variation in the size of individuals of the same species 

 taken at the same time points to more than one brood in the season, but they 

 are so difficult to rear that exact data on this point are lacking. In captivity, 

 Achorutes socialis Uzel and some other species lay only in the spring, while 



