STRUCTURE AND ECONOMY OF SPIDERS. 329 
ridion lineatum, and numerous other species do not 
usually survive the second winter after quitting the 
egg in this northern climate. 
A passage in the ‘ Introduction to Entomology,’ by 
Messrs. Kirby and Spence, fifth edition, vol. iv. 
letter xliv. p. 214, merits a brief notice; it is this :-— 
“Spiders are reputed to be subject to the stone: I do 
not say calculus in vesica; but we are informed by 
Lesser that Dr. John Franck having shut up fourteen 
spiders in a glass with some valerian root, one of 
them voided an ash-coloured calculus with small 
black dots.” This singular opinion seems to have 
originated in a misapprehension of an ordinary 
occurrence, which I shall proceed to explain. If the 
faeces of spiders, which consist of a white fluid com- 
prising black particles of greater density, happen 
when voided to be suspended in the webs or among 
the lines spun by these animals, they assume, under 
the influence of molecular attraction, the spherical 
figure common to fluids in general when similarly 
circumstanced, and soon becoming indurated by 
desiccation, a change of colour from white to grey or 
greyish brown spotted with black uniformly takes 
place ; and in this state they constitute, I doubt not, 
the substance which Dr. Franck mistook for a 
calculus. . 
Variations in the colour and size of spiders of the 
same kind, resulting from differences in age, sex, 
food, climate, and other conditions of a less obvious 
