BEHAVIOR OF SPIDERS AND OTHER INSECTS 397 



about the middle of September, the mosquito Calcx pipiens 

 becomes positively thigmotactic and seeks dark quarters. After 

 becoming acclimated to its surroundings, its normal negative 

 phototropism is entirely replaced by- positive thigmotropism. 

 At the approach of spring the mosquito becomes positively 

 phototropic up to a certain point. 



VISUAL SENSATIONS 



Hunter (63) thinks that form discrimination by animals is 

 always pattern discrimination. 



Seitz (91) discusses the vision of insects. 



Karl v. Frisch's (42) recent contribution is one of the best 

 studies extant on the color vision of insects. He arranged 

 thirty graded discs of cardboard, extending from white to black, 

 upon a rectangular piece of cardboard in such a manner that 

 it was possible to insert other discs of the same size among them. 

 So far as shades of grey were concerned, the discs were arranged 

 on the rectangle in an irregular manner. Two yellow discs, each 

 supporting a watchglass of honey, were placed among the grey 

 discs. After the bees had been collecting food from these yellow 

 discs for two days, they were removed and new yellow discs, 

 each supporting an empty watchglass, were placed on a different 

 part of the rectangle. Immediately these were visited by the 

 bees; but no attention was paid to the grey discs. Bees that 

 had been trained to forage from yellow, alighted on the yellow 

 pencil with which Frisch was taking notes. In a similar manner 

 bees were trained to forage from blue discs. Such bees, in four 

 minutes, made 282 visits to the blue discs and only three to the 

 grey. Empty watchglasses were now placed on the blue discs 

 and similar glasses, containing sweetened water, on the grey. 

 The bees attempted to feed from the empty dishes on the blue 

 discs, but paid no attention to the full ones on the grey. In like 

 manner an attempt was made to train bees to collect from red 

 discs. Such bees visited equally the red, dark grey and black 

 papers. Evidently bees have color vision, for they can dis- 

 tinguish yellow and blue from greys; but they are color blind 

 to red. 



On reading of these researches, Mrs. Ladd-Franklin (67) 

 wrote to Frisch and asked him to make some tests to see if 

 there was not a certain blue-green, as well as red, to which bees 



