354 APHANIPTERA. 



from them come worm-like maggots. These larvae have no feet, 

 but the last segment has two strong curved hooks. In a fortnight 

 or less some species spin a silken cocoon. (It was this, I fancy, 

 which made Aristotle speak of them as " egg-shaped" worms.) In 

 some species the larvae are said to live through the winter and not 

 pupate until the spring. Certainly, during the past winter, I have 

 had the greatest difficulty in obtaining any fleas. 



Regarding the parasites of fleas I know very little ; but only a 

 few days ago, on some fleas I took from a rat, I found some 

 minute white acari, which were to a wonderful degree tenacious 

 of life. I put the fleas into liquor potassae, which appeared to 

 kill them in about ten minutes ; but twenty-four hours later I found 

 an acarus walking about on the body of one of them to all appear- 

 ance none the worse ; the remaining acari had all disappeared. 



I have not been able to find any record of fossil fleas. The 

 geographical distribution of fleas seems to be world-wide ; they 

 are found from the Arctic regions to the equator. Darwin, in the 

 Voyage of the Beagle^''' writes of the mountains near Coquimbo : — 

 " I enjoyed my night's rest here from a reason which will not be 

 fully appreciated in England ; namely, the absence of fleas. The 

 rooms in Coquimbo swarm with them ; but they will not live here 

 at the height of only three or four thousand feet." This, he 

 states, cannot be on account of the trifling diminution of tempera- 

 ture at that height. They occur just as plentifully in the mountain 

 chalets of Switzerland as in the warmer valleys. 



Before bidding adieu to the fleas, I must just mention the 

 other family of Aphaniptera — the Sarcophsyllidce, of which fortu- 

 nately we have no representatives in this country. 



According to Taschenberg there appear to be only two or 

 three species, but it contains the famous, or rather the infamous, 

 " Jigger " {Sarcopsylla penetrans)^ an American pest, especially 

 abundant in the West Indies and in the north of South America. 

 It is often called the sand-flea. The males and the immature 

 females are no worse than other fleas ; it is the impregnated female 

 which is the chief trouble. She burrows under the skin of animals, 

 in the feet or under the toe-nails of man. There her body swells 

 to the size of a pea under the pressure of the eggs within her, 



* Voyage of Beagle^ p. 344. 



