730 THE EYE IN EVOLUTION 



to produce the fully-eyed male is not clear. Moreover, although their nest is under- 

 ground, these ants are nomadic on the surface and their armies, the members of which 

 are completely blind, are forever on the move. It is to be remembered that the 

 big-eyed, innocuous male driver ant is a gentle and relatively useless creature — merely 

 a stud animal with a momentary function as likely as not never to be fulfilled ; while 

 the monstrous regiment of his sisters ranks among the most ferocious and blood- 

 thirsty creatures the world knows. It has been suggested that these unsexed females 

 which march ahead against any obstacle and into any danger, which attack and devour 

 anything alive in their line of march, would find difficulty in maintaining the iron 

 discipline of their ranks if they were distracted by vision, and that blindness is therefore 

 an asset of evolutionary value to the ferociovxs and purj^osive female but not to the 

 idle and harmless male (Crompton, 1954). The suppression of eyes in this view (which 

 many would not accept) is positive, differing entirely from the mechanism which 

 usually indvices eyelessness. 



On the other hand, it may be that some other system of inter-communication 

 exists of which we have no knowledge, outside the visible limits of the electromagnetic 

 spectrvim. It is indeed difficult to conceive how otherwise the extraordinarily complex 

 activities within these underground cities could be conducted, not only as an ordered 

 routine bvit with coordinated variations to meet unexpected emergencies of construc- 

 tion or war with equal facility, in which each member of the community — cjueen, king, 

 soldier, policeman or worker — finds an appointed place. It may, indeed, be that eyes 

 have become useless owing to the development of senses other, and perhaps more 

 efficient, than our own. 



Fig. 876. — Ichthyophis. 



A subterranean burrowing Amphibian, limbless, somewhat resembling an earth- 

 worm ; the eyes are small, functionless and covered Ijy skin (head on right). 



Among Vertebrates, fossorial Amphibians, Reptiles and Mammals are 

 encountered ; in a sense some limicoline fishes (catfishes, etc.) which we have 

 already discussed might be brought into this category. 



Among Amphibians, the Csecilians (Apoda) form a peculiar archaic 

 group highly specialized for burro wmg (Fig. 876) — Ccecilia of South America, 

 Ichthyojjhis of Southern Asia, Hypogeophis of East Africa, Siphoiiops of 

 America ; with the exception of the aquatic Typhlonectes, all spend most of 

 their lives underground. Their most efficient sensory organ is a retractile 

 sensory tentacle situated at the anterior border of the orbit, while the eyes 

 are very small (less than 1 mm.) and can be useful only in light -detection. 



The minute eyes of the Crecilians are attached to the skin and lie in a roomy 

 orbit, largely filled by a Harderian gland which, however, is used to lubricate the 

 sensory tentacle ; the levator bvilbi muscle of Amphibians is vised as a compressor 

 of this gland to assist in its evacuation. Two of the other extra-ocular muscles are 

 commandeered to move the tentacle and have no action on the immobile eye, the 

 retractor bulbi acting as a retractor of the tentacle and the internal rectus as a retractor 

 of its sheath. The cornea is fused with the skin, there is no ciliary body or mesodermal 

 iris, the lens is large, spherical and usually cloudy, while the retina is provided only 



