1 905-1906.] The '■'Water-Flea" Scare in our City. 273 



to 30,000 in the space of a square yard, so that they were 

 literally present in millions." They are found by the sea- 

 shore, in woods, moors, and mosses, on garden gravel-paths, in 

 greenhouses, under flower-pots, and in numerous other situa- 

 tions. In all these places they act very much the part of 

 Nature's scavengers, living on decaying vegetable (and 

 animal X) matter. I can always secure a supply from a 

 Japanese Hare's-foot fern {Davallia hullata) grown as a hang- 

 ing plant, without a pot, and having the long rhizomes of 

 the fern plaited outside to enclose the soil. This form 

 of plant, known as a " design " by the nurserymen, when 

 plunged into water, liberates the spring -tails in dozens, 

 which then float ofif and congregate in little knots or groups 

 on the surface.-"^ 



The important question now remains. How has this " de- 

 graded " insect — or perhaps this " ancestral form " of insect, 

 as some scientists consider it to be — found its way into the 

 water-supply of our city ? To this there seems to be but one 

 answer, namely, that the eggs have been blown by the wind 

 or carried by rain-spates into the fire-hydrants of our streets, 

 and have there found a congenial breeding-place. We have 

 just seen how numerous and widespread the insects them- 

 selves are ; and that their eggs should be carried, along with 

 street-refuse, into these inviting hiding-places, need form no 

 cause of wonder. The type of hydrant known as the " ball " 

 form, which has been largely in use in our city for some fifty 

 years, is defective in this respect, that when the pressure 

 necessary in order to close it is taken away, an opening is at 

 once left in the hydrant box into which any foreign matter 

 may readily enter. To complete the mischief thus done, as 

 soon as the pressure returns any refuse which may have found 

 its way into the box enclosing the hydrant is swept through 

 the water-pipes, and so enters the cisterns. How much of 

 this semi-liquid mixture may have gone down the throats of 

 the citizens during the last half -century, no one can tell. 

 The appearance of these little scavengers in numbers has at 

 length saved the situation. " CoUembola," says Lord Ave- 



^ Mr Evans has very kindly examined some specimens of this spring-tail v?hich 

 I sent him, and has pronounced them to belong to the genus Lipura — a genus 

 very closely allied to Isotoma. 



