THE CANADIAN ENTOMOLOGIST. 177 



the centre of the umbel, it is quite invisible unless specially looked for. 

 Thus concealed, it waits until some insect — frequently a small bee, or a 

 butterfly of the genus Pamphila, settles on the flower — but no sooner is 

 the insect intent upon the nectar of the blossom, than the cunning Thomisid 

 has it in its grasp, and is sucking its life-juices away. On one occasion, 

 also, I found a white Thomisid spider seated on a white umbel, and 

 equally concealed here by its whiteness, it had secured and was feasting 

 on a bee. So far good. It may be argued that spiders of this family have 

 been accustomed to sit on flowers, and being variable in colour (as in fact 

 they are) natural selection has so arranged matters that yellow spiders pre- 

 side over yellow flowers, white over white, and so on. But perhaps, also, the 

 spider has " an eye for colour," since he (the yellow one) occasionally 

 sits on a small species of sunflowers which has yellow rays and a dark 

 brown disc — and here, although the spider always sits in the middle of a. 

 yellow umbel, he sits on the rays of this sunflower, knowing altogether 

 better than to expose himself to observation on the brown disc. But, to> 

 come to the point to be discussed, there is a species of geranium found 

 here ( Geranium fremontii Torrey,,) having pink flowers — yet the yellow- 

 spider sits on these, apparently unconcerned at the difference of colour. 

 Now, it is a curious thing, that throughout living organisms, whether birds 

 (e. g. Fringillidoe), mollusca (e. g. Tellinidce, Helicidce), insects (e. g. 

 Zygcenidce, Sesiidoj, Chelouiidce, Ic/ineumonidce), or plants, that the red 

 and yellow pigments seem to stand in this relation to one another, that 

 the red is a more complex form of the yellow, and hence occasionally reverts 

 to it, yellow being in all cases the primitive color. In Geranium, it is 

 true, there are not (to my knowledge) yellow-flowered varieties, but then r 

 there are both pink and yellow-flowered species of Oxalis, in the same 

 natural order. Therefore, it is conceivable that the yellow Thomisid first 

 came to sit on geranium flowers at the time when these were yellow, 

 and has continued the habit — but still, since it appears to understand the 

 difference between brown and yellow on the sunflower, why cannot it tell 

 that pink and yellow are not the same ? Does it not look as if, to this 

 spider, these colours were indistinguishable ? 



Also, the geranium-frequenting spiders do not starve, although to 

 human eye they are very easy to be seen — does not this, again, look as if 

 the insects frequenting those flowers could not distinguish between pink 

 and yellow, and so, not seeing the spider, fell unwittingly into its grasp ? 



