Urinary Excrement of Insects. 339 



minute portion of alvine excrementitious matter being mixed 

 with the urinous. In one instance, under the microscope, a 

 few very small prismatic crystals were seen mixed with the 

 granular matter, resembling those of phosphate of lime. The 

 proportional quantity in which tliis excrementitious matter is 

 voided is also remarkable. It suggests the idea that almost 

 the whole of the food of spiders is digested, and that their 

 principal secretion and excretion is the urinary. And, 

 further, as the food of these animals is entirely insects, and 

 chiefly flies (the smaller kinds of which they appear to de- 

 vour), and as I have been unable to detect any traces of 

 lithic acid in the excrement in question (an acid which it may 

 be inferred is contained in the cloaca of many of the insects 

 consumed), the idea is suggested that, in the digestive pro- 

 cess in the spider, this acid is either assimilated, so as to 

 form a part of the nutritive fluid, or is altered and converted 

 into zanthic oxide. 



Should further inquiry confirm the results I have obtained, 

 and should it be found, as it appears to me highly probable, 

 that the urinary secretion of spiders, in general, consists of 

 zanthic oxide, — a compound hitherto only rarely found, and 

 as a morbid production only, and confined to the human race, 

 it will be a curious fact established. 



In this tropical region, teeming with animal life, and 

 equally so with vegetable, the quality of the urinary excre- 

 ment of insects and of spiders, — considering the one as prin- 

 cipally lithate of ammonia, and the other as chiefly zanthic 

 oxide, — seem to be peculiarly in harmony with an adapta- 

 tion of means to ends, and an example of that happy economy 

 which is so often to be witnessed in the processes of nature. 

 Lithate of ammonia appears to be specially fitted to contri- 

 bute to form a part of the food of plants, and the same remark 

 will probably apply to the zanthic oxide. Both are only 

 slightly soluble in water. Both in their unmixed state ap- 

 pear to be rejected by animals of every description in search 

 of food. Ants here, which may be considered as the princi- 

 pal scavengers of the tropics, especially as regards putre- 

 scent animal matter, leave untouched, I have observed, the 

 urinary excrement both of insects and spiders. This exemp- 



