126 LIFE: ITS NATURE AND ORIGIN 



Thus the British 'wood-ant' (Formica rufa) has a smaller and a larger 

 race of workers ('minor' and 'major' forms), while in Ponera we find 

 a blind race of workers and another race provided with eyes, and in 

 Atta, Ecitron and other genera, four or five forms of workers are 

 produced, the largest of which, with huge heads and elongate trench- 

 ant mandibles, are known as the 'soldier' caste. The development of 

 such diversely formed insects as the offspring of the unmodified females 

 which show none of their peculiarities, raises many points of difficulty 

 for students of heredity. It is thought that the differences are, in part 

 at least, due to differences in the nature of the food supplied to larvae, 

 which are apparently all alike. But the ovaries of worker ants are in 

 some cases sufficiently developed for the production of eggs, which 

 may give rise parthenogenetically to male, queen or worker offspring." 



Discussing the role of chemoreception in the ability of rattle- 

 snakes to recognize ophidian enemies, C. M. Bogert 68 states that 

 although rattlesnakes when confronted by man or by domesticated 

 animals, normally assume a coiled defense attitude, with head 

 raised ready to strike, immediately after exposure to ophiphagous 

 king-snakes they react to contact and to visual stimuli only by 

 assuming a characteristic "king-snake defense posture": head and 

 tail flat on the ground, with the body arched to a high loop with 

 which to strike a defensive blow. Rattlesnakes assumed this char- 

 acteristic posture when placed in a receptable that had previously 

 held king-snakes, and also when a clean stick that had been rubbed 

 on the back of a king-snake was held near. The activating sub- 

 stance is apparently taken up by the tongue and conveyed to 

 Jacobson's organ, which contains olfactory cells; and the response 

 was evoked by visual or by contact stimuli as long as three hours 

 after receipt of the original olfactory stimulus. Apparently some 

 trace of a volatile substance powerfully conditions the behavior 

 of the rattlesnake. 



H. S. Raper and collaborators have shown 69 that the enzyme 

 tyrosinase catalyzes the conversion of tyrosine (an amino acid con- 

 stituent of some proteins) into 3, 4-dihydroxyphenylalanine, called 

 dopa for short. Dopa is then oxidized by the same enzyme to a 

 red indole derivative which spontaneously changes to melanin, a 

 pigment which gives hair and skin a dark brown or black color. 

 Factors affecting the activation of the precursor of tyrosinase have 

 been studied by J. H. Bodine and collaborators. 70 The pro- 

 enzyme separates in the aqueous layer obtained by ultracentri- 

 fuging mashed grasshopper eggs, and is activated when added to 



