32 EXPOSED AND CONCEALED ANIMALS 



genus Machilis which is found living on the 

 moist and shaded surfaces of lichen-covered tree- 

 trunks and rocks, the mottled appearance of 

 which the insects closely resemble. It is doubt- 

 less in virtue of this singular property of con- 

 cealment that so many of the primitive forms 

 have survived to the present day to be at once 

 the delight and bewilderment of the systematist. 

 The noxious arthropods, which are only too 

 familiar in certain quarters, are also cryptozoic, 

 but it may be satisfactory to note that they are 

 not primitive ; they belong irreclaimably to the 

 things of darkness. 



Earthworms are well known to every horti- 

 culturist and tiller of the soil, and to every one 

 who has read Darwin's famous book about them, 

 but the other cryptozoa (sensu stricto) are hardly 

 known outside the ranks of specialists. Darwin 

 estimated that in many parts of England more 

 than ten tons of dry earth annually passes through 

 the bodies of earthworms on each acre of land. 

 Equally impressive figures could be given to 

 show the amount of sand-casting performed by 

 the lugworms (Arenicolidce) on some temperate 

 shores, and by the Enteropneusta (Balano- 

 glossus) on some tropical shores. 



So far I have referred almost exclusively to 

 land animals because they are most in evidence 

 by the effects which they produce in relation to 

 husbandry. Predatory aquatic animals, especially 



