BOOK-LOUSE AND SILVER-FISH INSECT 311 



to the Royal Society, in which he roughly described and 

 figured the insect, and detailed his own observations. 

 These papers may be found in the Philosophical Trans- 

 actions for the years 1701 and 1704. He is careful to 

 distinguish the insect, as regards its form and the 

 character of its beating, from the ticking beetle above 

 referred to, the habits and form of which had been 

 described and illustrated in a paper from which we have 

 already quoted, and which was presented to the same 

 society a short time before by Mr. Benjamin Allen. 

 Derham gives the subject of his observations the name 

 of Pediculus pulsatorius (the drumming-louse), but there 

 can be little doubt that it was the same as that now 

 called Atropos divinatoria. 



He especially notices its minute size, saying that he 

 was obliged to use a magnifying glass to watch its move- 

 ments and habits. He points out, further, that whilst 

 the death-watch beetle beats only seven or eight strokes 

 at a time, and quicker, "the other will beat some hours 

 together without intermission, and his strokes are more 

 leisurely, and like the beats of a watch." The ticking 

 was hardly ever heard except in July and August, and 

 was much more frequent in some seasons than in others. 

 In the year 1702 "they ticked very much, scarce ever 

 ceasing day or night," but the next year they were far 

 less active, and the sound was rarely heard. The insect 

 produced the sound by beating the front part of the 

 head against the object on which it was resting j and 

 Derham regarded it as in some way connected with the 

 mating period a sort of love-call which would account 

 for its being heard only at certain seasons. These two 

 points form, indeed, as already mentioned, the correct 

 explanation of the ticking of the true death-watch, and 

 so far are, therefore, possibly operative causes in other 



