55^ Causes and Course of Organic Evolution 



one on this planet, and from the point of view of intelhgence 

 and power of cooperating in the formation of social communi- 

 ties is surpassed but by the Vertebrata" (179: 255). Some 

 families of the Arachnida, like the ticks, the mites, and the 

 gall-mites, may be more or less degraded offshoots from higher 

 orders of the Class, but the scorpions and spiders specially 

 concern us at present. 



The viviparous habit, and the relation of mother to offspring, 

 when these are hatched, indicate a degree of parental regard 

 that is the basis for some of the finer mental qualities. The 

 chemotactic and mechanotactic functions are highly developed, 

 and it would be an interesting inquiry to ascertain to what 

 extent the large dorsal neural mass is olfactory or chemotactic 

 in function. Fabre's account of the scorpioid genus Buthus 

 at once suggests a decided atrophy of some senses, and a high 

 development of others, specially the thigmo- or mechanotactic. 

 But the studies of McCook, Fabre, and the Peckhams, amongst 

 others, show that the spiders in spite of their solitary lives 

 have evolved high instinctive relations, that verge in not a 

 few cases on simpler reasoning powers. For in making often 

 distant but secure ties for the webs, in methods of swathing 

 captured prey, in evolving and continuing mimetic resemblances 

 between nest and environal objects, in cleaning their persons, 

 and many other acts, there is such an interlinking of instinctive 

 and reasoning qualities that man himself has to learn greatly 

 more about them, and has to interpret more keenly and analyt- 

 ically, before final conclusions can be reached. But the want 

 of cooperative effort in the entire group has undoubtedly pre- 

 vented the development of those associative mental conditions 

 which have so largely contributed to the elevation of other 

 and higher groups like those next to be mentioned. 



The third series of highly evolved animals is that of the bees 

 and ants amongst the Insecta. In many families of insects 

 the limbs and accessory mouth organs are used largely or 

 wholly for progression and mechanotactic action. The eyes 

 are usually well, or even very highly developed, but doubt 

 exists as to the location of olfactory and auditory organs. The 



