COLLEMBOLA 



225 



ORDER COLLEMBOLA* 



The Spring-Tails 



The members of this order resemble the Thysanura in being wingless 

 insects in which the wingless condition is believed to be a primitive one, 

 there being no indication that they have descended from winged ancestors, 

 and in that the adtdt insects resemble the young in form. They differ 



Fig. 230. — Side view of Tomocerus plumbens: co, coUophore; c, catch; s spring. 

 (Aftar Willem.) 



from the Thysanura as follows: the abdominal segments are reduced in 

 number, there being only six of them; the first abdcnninal segment bears 

 a ventral tube, the coUophore, furnished with a pair of eversible sacs which 

 assist the insects in walking on smooth surfaces; 

 the fourth abdominal segment usually bears a 

 pair of appendages, which constitute a spring- 

 ing organ; and the third abdominal segment 

 usually bears a short pair of appendages, the 

 catch, which hold the spring when it is folded 

 under the abdomen. 



The common name spring-tails has been 

 appHed to these insects on account of the 

 caudal springing organ that is possessed by 

 most members of the order. The spring- 

 tails are minute insects, often of microscopic 

 size and rarely as large as 5 mm. in length. 

 Most of the species live on decaying matter. 

 These insects are common under stones 

 and decayed leaves and wood, in the chinks 

 and crevices of bark, among moss, and on 

 herbage in damp places. Sometimes they 

 occur abundantly in winter on the surface 



Fig. 231. — An ommatid- 

 ium of Podiira aqual- 

 ica. (After Willem.) 



*Collembola: 

 collophores. 



colla {K6X\a), glue; embolon {iix^oKov), a bolt, bar; — from their 



