INSECTA 465 



nearly complete fusion of a pair of appendages has resulted in the 

 formation of the hamula, which engages the furcula prior to leaping. 

 The latter is a forked structure representing a pair of limbs of the 4th 

 segment (Fig. 323). By contraction of the extensor muscles of the 

 furcula the latter is pulled down out of contact with the hamula and 

 the animal is propelled forwards into the air. 



The absence of tracheae is a secondary feature due to the small size 

 of the animals rendering surface respiration sufficient for their mode 

 of life. 



Collembola have a wide distribution. They are found along the 

 sea shore between tidemarks and submerged by each tide, e.g. 

 Anurida maritima. Common aquatic forms are denizens of fresh 

 waters, e.g. Podura aquatica. They have been reported to be so 



1^^: 



TTlO 



Fig. 323. A, Axelsonia (Collembola). B, Hamula of Tomoceros showing 

 c. basal piece, and r. its rami. From Imms, after Carpenter and Folsom. 

 p. ocular pigmented area; v. ventral tube; h. hamula; m., d. and mc. caudal 

 furcula. 



abundant in Arctic zones as almost to cover the snow, and in Europe 

 sometimes to be present in such large numbers that the progress of 

 railway trains is impeded owing to their having prevented the wheels 

 from gripping the rails. 



Order PROTURA 



Minute insects without wings, eyes or antennae ; with piercing mouth 

 parts deeply inserted in the head capsule ; with abdomen of twelve 

 segments, the first three of which bear papillae. 



This is a small group of doubtful affinities. Its members are found 

 in decaying organic matter. The fact that on hatching the abdomen 

 is 9-segmented and that subsequent moults bring about the full 

 number of segments is regarded by some authorities as sufficient 

 ground for their inclusion in a class distinct from the Insecta. An 

 example is Acerentomum doderoi of Europe. 



