BOOK-LOUSE'AND SILVER-FISH INSECT 319 



to have been generally noticed, viz., the present one; 

 a similarly shaped but considerably larger brown one, 

 found amongst heaps of stones near the coast; and a 

 minute, pale, yellowish-white creature with two long tails, 

 which may be found under stones that have lain long on 

 soft damp ground. A special interest attaches to this last 

 (Campodea staphyUnus), seeing that, in the words of Sir 

 John Lubbock, "there are good grounds for considering 

 that the various types of insects are descended from 

 ancestors more or less resembling the genus Campodea. 

 ... If these views are correct, the genus Campodea 

 must be regarded as a form of remarkable interest, 

 since it is the living representative of a primaeval 

 type, from which not only the Collembola and Thysanura, 

 but the other great orders of insects have derived 

 their origin." Some naturalists regard the Thysanura 

 as allied to the Neuroptera, including them amongst 

 that section of the order called Pseudo-Neuroptera. 



Little need be said as to the digestive system, since it 

 is constructed on the usual insect type. The alimentary 

 canal is a straight tube running through the body. The 

 gullet enlarges into a crop, which is succeeded by a 

 grinding apparatus, in the form of a globular gizzard 

 furnished with six tooth -like projections; after this 

 comes the true or digestive stomach, succeeded again by 

 the intestine, at first narrow, but in its hinder part 

 broader; the Malpighian tubules are four in number. 

 When contemplating the functions of the silver fish in 

 nature, Hooke, the author of the Micrographia, falls 

 into the following curious reflections, very characteristic 

 of the physiological ideas of the times in which he lived : 

 " When I consider what a heap of Sawdust or chips this 

 little creature (which is one of the teeth of Time) con- 

 veys into its intrals, I cannot chuse but remember and 



