June, 1905] Packard: Color in a Flower Spider. 93 



vidual, and are not transmitted to the offspring, beyond the fact that 

 they are due to differences in the colorational environment, t. e. , the 

 white, or yellow or pink hues of the flowers in which the spider hides 

 or on which it rests. 



The explanation of the cause must be sought in what we regard as 

 a parallel case in the experiments initiated by T. W. Wood* in 1867, 

 and greatly extended by Professor Poulton,* as described in his able 

 essay "On the color relations between certain lepidopterous pupae, 

 and the variously colored surfaces immediately surrounding them." 

 Mr. Wood found as the result of his experment that " the skin of the 

 pupa for a few hours after the caterpillar's skin has been shed is ' pho- 

 tographically sensitive,' " and "as might be expected, by putting the 

 specimens in the sunshine at the time of changing, and surrounding 

 them as much as possible with any desired colour, the most successful 

 results have been obtained." 



Professor Meldola has pointed out, says Poulton, that the theory of 

 the moist, fresh, pupal surface as "photographically sensitive" was 

 obviously a metaphor borrowed from the sensitive plate of photog- 

 raphy and that there can be no real analogy between the two 

 processes. Poulton concludes that the problem is essentially a physio- 

 logical one, and that the physico-chemical changes are " merely the 

 results of far more complicated physiological processes." 



The question arises Avhether the change in M. vatia is connected 

 with the molting period, but I have no observations which directly 

 prove this. It is well known that many spiders with nearly each molt 

 appear in different colors, or undergo some change in the markings. 



Summary of Results of My Own Observations. 



1. In the early part of the summer (June and July) when the 

 greater mass of flowers are the white fleabane and the ox-eye (the 

 wild rose and buttercups excepted) the spiders (M. vatia) are white 

 and no yellow ones were detected. 



2. Later in the season, towards the end of July (July 30-31), and 

 early in August when the golden rod in Maine begins to flower, a few 

 of the spiders are yellow, but by the middle of the month and through 

 September they are almost without exception yellow, varying from a 

 pale to a deep hue, probably due to the length of time they have been 



* Trans. Ent. Soc. London, 1867, p. XCIX-CI. 



| Philosophical Trans. Royal Soc. London, vol. 178, 18S7, p. 31 1. 



