MATING HABITS. 235 



male frequently mounts the back of another male, but I have never seen one 

 attempt to copulate. When mutilated, however, they try most vigorously 

 and persistently for a long time to effect copulation with other males, thus 

 showing their inability to recognize the difference between the sexes without 

 the help of their olfactory organs. 



Similar results were obtained by the experiment of painting the antennae 

 and palpse with paraffin, balsam, shellac, and other substances which prevent 

 the use of the olfactory organs, but do not give the shock occasioned by the 

 removal of the antennae and palpae. Beetles thus painted were quite as unable 

 to distinguish the sex of their companions as were those without these organs ; 

 but when this coating of paraffin was removed they could distinguish the other 

 sex as readily as those beetles that had not been experimented with. 



I also tried the experiment of painting the bodies of the animals black, red, 

 white, green, and other colors, using largely individuals of the species decern- 

 lineata, miiltitceniata, dilecta, undecimlineata,violescens, and lacerata. As far 

 as I have been able to observe, the giving to either male or female a color not 

 natural to it had no influence whatsoever upon the mating in any species, 

 neither when the color was applied to one sex alone nor when it was applied 

 to both. 



Experiments were tried in which the abdomen of the female was covered 

 with shellac, paraffin, or other substances which would prevent the odor of the 

 sexual glands from escaping; the result was that the males passed by the 

 females so treated without recognizing them as females at all. Experiments 

 with various mutilations were tried, but in all the same result was obtained, 

 that if the olfactory organs and the scent glands remained intact the sexes 

 unerringly recognized each other; but any interference with either of these 

 organs at once prevented the recognition of the opposite sex. In these 

 beetles, as in Lepidoptera (Mayer, 1900), sex recognition is accomplished 

 solely through the olfactory organs and scent glands, the colors playing no 

 part whatsoever in the process. Whether these glands vary or not it has not 

 been possible for me to demonstrate, although there is no reason why they 

 should not show variation in the same manner as do other characters of the 

 body. If there is a variation in the scent glands either in number, in the 

 strength of their secretions, or in the ability of the male to perceive the odor, 

 it is not great enough to produce any observable selection in the mating of 

 those beetles which have come under my observation. 



In all the species of the genus Leptinotarsa copulation occurs many times 

 in the reproductive period, and with different individuals, so that often by the 

 time the first eggs are laid the receptaculum seminis contains spermatozoa of 

 several different males, and hence the offspring of one female may have 

 several different males for the other parent. This results in a great com- 

 mingling of the species in reproduction, and a consequent tendency to keep 



