TYPE TB ACHE AT A. 503 



same form are interesting in being destitute of longitudinal 

 and transverse anastomoses. 



Lepisma is frequently found in houses, in attics and similar 

 places, feeding upon woollen, linen, and other fabrics, but also 

 on meal or sugar. Campodea (Fig. 232), on the other hand, is 

 to be found under stones or dried leaves and is a small white 

 form, by no means uncommon. 



2. Order Collembola. 



The Collembola are distinguished from the Thysanura by 

 the abdomen consisting usually of but six segments, and in 

 some cases the number is even smaller. The body in Podura 

 is covered with scales, and the terminal segment of the body 

 is usually provided with two processes which may be bent up 

 underneath the abdomen and then suddenly extended, pro- 

 pelling the insect to a considerable distance. These structures 

 are absent in the adult Anurida, but occur in young speci- 

 mens, and their occurrence and function have suggested the 

 popular name of Spring-tails applied to the order. Neither 

 abdominal appendages nor coxal glands occur, but the first 

 segment bears a peculiar organ, having in Anurida the form 

 of a saccular protrusion, which is probably adhesive in func- 

 tion. The antennae are usually short, and bear in some forms 

 an antennal sense-organ similar to that of Campodea; the 

 mouth-parts are biting, but frequently much reduced in size. 



The nervous system is usually much concentrated, there 

 being in Anurida but three postoral ganglia situated in the 

 thorax, the abdominal ganglia having evidently fused with 

 the last thoracic. Simple eyes are present in varying numbers, 

 but compound eyes never occur. A peculiar organ lying be- 

 hind the bases of the antennae, and hence termed the post- 

 antennal organ, occurs, and has been supposed to be a sense- 

 organ, but further information is required concerning it. 

 Tracheae are usually present, though quite wanting in Anurida. 



The genus Podura is to be found, sometimes in consider- 

 able numbers on the surface of standing water in the early 

 spring, while other forms occur in damp earth or under bark. 

 Anurida is found upon the seashore underneath stones just 

 above tide-mark. 



