SENSES of insects: sight 213 



"I could quote further from the work of Forel, but limit myself to the preceding. 

 I thank him for giving me the opportunity to prove that, even in supposing all the 

 criticisms of which he is not sparing to be absolutely well founded, the results of my 

 studies on the relations between insects and flowers are not as worthless as some pre- 

 tend and that they do lead to the refutation of this part of the floral theory of Hermann 

 Mliller and his school, who attribute to the brilliance of flowers, to their colors more 

 or less striking, an important role in the attraction of insects and consequently in 

 fecundation (1902:424). 



"Two corollaries may be derived from this fact: the first is that the attractive 

 r61e of the form and color of the floral envelopes is either null or nearly so; the second 

 is that other causes than the attraction of colored surfaces is necessary to bring pol- 

 linators to flowers and to cause them to return, such as an odor pleasing to insects 

 and a sugary liquid." "In r6sum£, the present investigation but confirms the thesis 

 advanced in 1897 in the following words: 'Insects seeking pollen or nectar are guided 

 to the flowers that contain these substances in only a subordinate degree by sight. 

 They are guided in an assured manner to such flowers by some other sense than vision 

 and this can only be the sense of smell' " (1910:51). 



Conclusions as to Plateau's views. — The admiration felt for Plateau's 

 frank admission that he had been wrong in assigning an exaggerated im- 

 portance to the sense of smell in attraction is more or less eclipsed by the 

 fact that this was never again referred to in his later papers, in which 

 he returned finally to his original view that the attractive role of color 

 is null or nearly so. In spite of Plateau's originality, industry, and patience, 

 the bias in favor of odor and against color pervaded all his researches, 

 blinding him to many faults of execution and leading him to unwarranted 

 conclusions. How dominant this prejudice was is shown by the fact that 

 within six pages after his apology for exaggerating the r61e of smell in at- 

 traction, he states that his studies refute the view of Mueller that color 

 plays an important part in this process. This also led him frequently 

 to overlook facts and results that were not in accord with his views, and to 

 make gratuitous assumptions as to the work of other investigators. A 

 second great fault of his experiments was the failure to insist upon the 

 regular use of controls, with the consequence that the results were often 

 open to any interpretation desired. With this went the failure to realize 

 that time, place, and conditions work great differences in response, and 

 that this was usually the explanation of the discrepancies between his 

 results and those of his critics, rather than carelessness or lack of thought 

 on their part. Finally, as Forel in particular insisted, he paid practically 

 no attention at first to the importance of habit and memory, and gave 

 them too little consideration throughout. In spite of all this, he deserves 

 great credit as the pioneer in experimental pollination, as an indefatigable 

 investigator, and a good-natured and courteous opponent. 



SENSES OF INSECTS. 

 SIGHT. 



The mosaic theory. — Forel (1886:10) emphasized the fact that the 

 structural studies of Grenacher (1874) and the physiological ones of Exner 

 (1875) led them to revive the earlier theory of Muller. This was not 

 that each facet formed an image, as Gottsche thought to have demon- 

 strated, but that the insect perceives a more or less clear image of the 



