236 HABITS AND INSTINCTS IN LEPTINOTARSA. 



the species in a mediocre condition by decreasing greatly the probability of 

 extreme individuals arising in any great numbers through their exclusive 

 breeding. 



Although copulation is accomplished with ease and without ceremony in 

 these beetles, it is not effected unless the conditions of existence are proper 

 for the act, or nearly so. The reason for its failure is largely, if not entirely, 

 the non-development of the germ-cell, any change in the normal rhythm of 

 reproduction being usually associated with changes in the environment, such 

 as excessive heat, cold, or moisture. 



The laying of the eggs does not present any features of special interest, 

 excepting that if the conditions of existence are too extreme the eggs, although 

 they may be fully formed and fertilized, are not laid, but are retained in the 

 passages of the female reproductive organs until they are resorbed, or, as 

 more frequently happens, until the female dies. This failure to deposit the 

 eggs seems to be caused solely either by the drying of the secretions or by the 

 inability of the female to produce them in the accessory glands. 



In the normal laying of the eggs in deccmlineata the female selects a proper 

 spot, and, raising her body high upon the legs, protrudes the posterior seg- 

 ments, opens slightly the genital plates, and, touching the tip of the abdomen 

 to the leaf, allows a drop of a yellow oily fluid to escape ; then as the abdomen 

 is slightly raised the egg protrudes and is fixed by its posterior pole in the 

 drop of fluid already deposited. The fluid now hardens rapidly and cements 

 the egg in place. One egg having been deposited, the female moves along a 

 slight distance, and there places another by the side of the first, and so on until 

 there is a row of from five to ten eggs in a nearly straight line on the leaf. A 

 second, third, fourth, and often as many as ten rows are thus laid, each of 

 which is more or less closely placed to the previously laid rows, and forms 

 therewith a compact bunch. I have observed the egg-laying in some 20 spe- 

 cies of this genus, and in all the procedure is the same. All the eggs that are 

 ripe at a given time may be deposited in one spot, or the beetle may lay a few 

 and then move on to another place to deposit a few more, and thus the 30 to 

 75 e gg s which mature at one time in these beetles may be laid on a half dozen 

 different plants. 



In all of these beetles the eggs are developed in batches, each of which is 

 laid before another is developed. The average number of eggs laid by the 

 females in this genus is 375, although there is considerable variation both in 

 the number of eggs laid by the different species and in the number of batches. 



The data on hand along this line are brought together in table 104, on 

 the following page. 



