ANALYTICAL INDEX. 149 



Page. 



The head of a planaria lost and renewed, 65 



Three heads on one animal, ib. 



Experiments to obtain redundant organs, 67 



Spontaneous division and renewal of parts, 69 



A supernumerary head may be produced by experiment, ib. 



Purpose of nature in reproductions, 70 



Sensorium of Planariae, , 71 



Two heads are frequently of opposite inclinations, . . . ib. 

 A second head, artificially produced, grows as large as 



its fellow, 73 



An incision in the side of the Planaria produces a su- 

 pernumerary head, » 74. 



Artificial regeneration is accomplished with greater dif- 

 ficulty than reproduction by natural division, .... 76 

 Is there a certain point from which either a head or a 



tail Avill be generated ? 77 



Resemblances to artificial monstrosities are sometimes 



found in the natural state, 79 



A tendency to action prognosticates the regeneration of 



a head, 80 



Natural monstrosities, 82 



The source of monstrosity is obscure, 84 



Planaria Arethusa, 85 



Errors of naturalists, ib. 



Animals disappear from their wonted abodes, 87 



Description of the Arethusa, 88 



Varieties, 89 



Eyes, 92 



Proboscis, 93 



Its singular situation, 96 



It is of gelatinous consistence, 98 



Its extreme flexibility, 100 



Observers are liable to deception, 102 



Propagation of the Planaria Ai-ethusa, 103 



A fragment separates from the body, 105 



Period requisite for regeneration, 106 



Complete animals from fragments are small, ib. 



