206 PRINCIPLES AND CONCLUSIONS. 



a more or less different expression of physiologically similar functions must 

 result from organs so differently constituted. 



As a consequence of what has been said, a part of the teaching of Sprengel 

 as to the ecological significance of the color of flowers can be accepted by 

 modern flower biology without modification. One reservation must be made, 

 however, to the effect that the two insects so far investigated, the honey-bee 

 and the bombyliad, possess a different optical perception of what appears 

 to us as pure red or blue-green in color and that in consequence neither of 

 these colors can exert an attractive action on these insects in connection 

 with pollination. However, the questions as to the nature of insect vision 

 and the ecological significance of the details of color and marking in flowers 

 can not be conclusively answered with our present knowledge. 



Vision and flower behavior of Macroglossa stellatarum. — The sec- 

 ond half of Knoll's monograph on insects and flowers treats of the response 

 of the hawk-moth to light and color, as well as to flowers, under the follow- 

 ing main captions: (1) observations on the life-history of Macroglossa; (2) 

 experiments on the vision of Macroglossa; (3) the food instinct in Macro- 

 glossa and its evaluation for the study of the color sense; (4) experiments 

 with freshly hatched moths; (5) the behavior of the female during the period 

 of egg deposit; (6) flower visits and fragrance; (7) critique of the experi- 

 ments of Plateau (p. 164); (8) notes on other Lepidoptera; (9) summary. 



In its flights for nectar, Macroglossa observes objects of a certain optical 

 quality, but not those of a different one. In addition to the dark colors, 

 it often visits also the paler ones and pure white, but takes no notice of 

 green plant parts, and just as little of the gray, black, or brown objects of 

 its environment. With the hawk-moth, as with the honey-bee and the 

 bombyliad, two groups of colors come into especial consideration, namely, 

 blue and yellow. When it has obtained its nectar for some time solely 

 from an object of a definite optical character, under certain conditions 

 there appears an association with such an object. In the attraction of this 

 moth from a distance the fragrance of flowers plays no part, as this appears 

 to be true also for the immediate proximity of the flower. This result was 

 entirely unexpected, as it has been generally assumed in flower biology 

 that the marked fragrance of many flowers was a direct adaptation to the 

 hawk-moths. However, this particular species does not lack the faculty of 

 perceiving plant odors, since the odor of Galium leads the female to deposit 

 her eggs upon it. 



A newly hatched hawk-moth flies directly to certain flowers, in spite of 

 the fact that it has had no individual experience with them. In doing 

 this it distinguishes the color of the blue and yellow groups from green and 

 the various grays. Thus, there is present in the inexperienced moth a 

 predilection for objects of a certain optical effect. This effect is given in 

 nature only by flowers, so that the young insect may go quickly to its food 

 in consequence. The action of certain optical stimuli in the process of 

 flying to the flowers and the consequent possibility of acquiring experience 

 by means of vision furnishes the basis for a part of the constancy of the 

 hawk-moth. This utilization of animal experience has already been made 

 by other investigators in this field, notably by Frisch with the honey-bee. 

 A comparison of the results shows that there is no essential difference be- 



