THYSANURA. -657 



incredible numbers after floods ; others, as Anurida maritima,* 

 are marine, living on the water of rock pools along our coast. 

 When the tide rises they retire to crevices in the rocks, but they 

 can survive long periods of immersion. A considerable number of 

 species have been taken in both Polar regions and they are com- 

 mon on snow and glaciers, which at times are blackened by 

 their countless numbers. The group is practically cosmopolitan, 

 though they seem on the whole to avoid warm districts. They 

 are said to live on organic debris of all kinds. Lubbock recog- 

 nized six families, but these have more recently been reduced to 

 three : 



Fam. 1. Smynthuridae. Bodies globular, devoid of scales and with 

 a considerable fusion of segments ; the apparent thorax small ; antennae 

 elbowed ; spring borne by fifth abdominal segment ; tracheal system 

 present. This family includes the Smynthuridae and Papiriidae of 

 Lubbock. Many of the members haunt 

 bushes and undergrowth. Smynthurus ; 

 Papirius. 



Fam. 2. Poduridae. Elongate bodies 

 not swollen ; spring on fourth abdominal 

 segment or in the Degeerides ( = Lub- 

 bock's family Degeeridae) on , the fifth. 

 These forms somewhat resemble minute 



caterpillars and are often highly coloured. FlG - M--Podura 



Podura ; Isotoma ; Corynotlirix. 



Fam. 3. Lipuridae. No spring. Slowly crawling minute creatures. 

 This includes the Lipuridae and Anouridae of Lubbock. Anoura has 

 very much modified mouth-parts, and its mouth is described as suctorial, 

 whilst that of Lipura is mandibulate. 



Order 2. THYSANUKA. f 



The abdomen shows ten segments and there is no ventral pro- 

 trusible tube or springing apparatus ; wingless ; with long multi- 

 segmented antennae and sometimes compound eyes. Cerci anales 

 on last abdominal segment. 



The Thy sanura, sometimes termed "bristle-tails," are insects 

 of moderate size. They have no trace of wings, and the prothorax 

 is often the largest segment in the body. Usually they move 

 actively, and tarsi are present on the legs. The abdomen 



* Anurida, A. D. Imms, Liverpool Marine Biological Committee 

 Memoirs, xiii, 1906. 



t Grassi, Mem. Ace. Lincei Rome (4), iv, p. 543, 1888 ; and Oude- 

 mans, Bijdr. Dierkunde, xvi, p. 147, 1888. Escherich, Zoologica, Heft 

 xliii. Silvestri, Zool. Jahrb. Suppl. vi, 1905, p. 7 4. 



Z III U U 



