630 LIFE : OUTLINES OF GENERAL BIOLOGY 



must remember that this "dirigible dog with the selenium eyes" 

 is very far away from the real dog we know. When we compare an 

 animal to a machine, we are apt to be more wrong than right. The 

 animal may be a machine, but it is a self-stoking, self -repairing, 

 self-regulating, self-preservative machine. Mr. Hammond's clever 

 machine has a human idea inside it, but it was put there by an 

 outside mind; whereas the dog has a mind of its own. The strictly 

 mechanistic view of life can never get beyond such Frankenstein 

 devices. 



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Diagrams of Keflex Action, (A) in an Invertebrate, and (B) 

 Modified, with permission, from Bayliss. 



a Vertebrate. 



(VIII) REFLEXES- At a slightly lower level arc reflex actions. 

 These, like instincts, deptmd on a pre-established neuro-muscular 

 chain, with a varying number of links, though typically with four. 

 As we have explained in the section on the nervous system, these 

 typical four arc: (i) the sensory neurons (5), (2) the associative or 

 communicating neurons {A), (3) the motor neurons (M), and (4) the 

 effector {E) muscle-cells which contract, or the gland-cells which 

 secrete. We need not re|x^at the familiar story; but a distinction 

 must be drawn between simple and com|x)und reflex actions. 

 When a sea-anemone closes its tentacles on one's finger, that is a 

 simple reflex action, involving only two links — the superficial 



