PRESENT KNOWLEDGE OF THE PROTURA. 231 



Genus 2. — Acerentulus. Labrum not produced. Mandible without 

 long style. Maxillary palps 3-jointed. Labial palps 

 2-jointed, but the basal joint is very indistinct. 

 Six species.—^, confinis, Berlese [3] ; A. tiarneus, 

 Berlese [4] ; A. ccphalotes, Berlese [3] ; A. gracilis, 

 Berlese [4] ; ^. miniimcs, Berlese [3] ; ^. perpusillus 

 Berlese [5] . 

 Family II. — Eosentomid^. Tracheal system present. Three pairs 

 of abdominal appendages, larger than in the 

 AcereJitomidce, and all 2-jointed. Palps as in 

 Acerentulus. 

 Genus 3. — Eosentomon. With the characters of the family. 



Seven species and one variety. — E. transitorum, Berlese 

 [3] ; E. ribagai, Berlese [5] ; E. Wheeleri and var. 

 incxicana, Silvestri [19] ; E. (Protapteron) indicum, 

 Schepotieff [16J ; E. Silvestrti, Kimsky-Korsakow 

 [14] ; E. germanicum, Prell [12] ; E. jabanicum, 

 Berlese [6] . 



Both species, which I have taken in England, belong to the 

 genus Eosentomon, but representatives of all three genera have 

 been taken by Mr. Bagnall. 



Abroad their known distribution is being rapidly extended, 

 and now includes Europe : Italy (Berlese, Silvestri), Russia, 

 Austria, Finland (Rimsky-Korsakow), Norway (Prell), Sweden 

 (Traghardt), Germany (Borner, Prell, Rimsky-Korsakow); 

 Asia : India (Schepotieff) ; America : United States, Mexico 

 (Silvestri). There is no doubt that within the next few years 

 they will be found over a still greater area. 



My specimens have been collected in either 70 per cent, 

 alcohol or Bouin's picro-formal (the latter for section-cutting), 

 and double staining the whole insect with methylene blue and 

 eosin has given fair results. The abdomen should be pricked 

 with a fine needle to facilitate staining. 



Rimsky-Korsakow [14] suggests killing with boiling water or 

 Gilson's fluid, and stains with dilute borax-carmine in 75 per 

 cent, alcohol. Schepotieff used concentrated sublimate solution 

 or Gilson's fluid, and Berlese uses hot acetic acid to produce 

 extension of the mouth-parts and genitalia. The other writers, 

 following an unfortunate custom among many entomologists, 

 give no particulars of their methods. 



Bibliography. 



1. Bagnall, R. S. : Some Primitive British Insects. I. TheProtura. 



Knowledge (London), New Series, vol. ix., 

 1912, p. 215. 



2. Becker, E. : Zum Bau des Post-antennalorgans der Collembola. 



Zeit. f. wissenschaft. Zool., xciv., 1910, pp. 

 327-399. 



3. Berlese, A. : Nuovo Acerentomidi. Redia v., 1908, pp. 16-19. 



