2o8 THE BIOLOGY OF INSECTS 



and only showing slight movements of the body or limbs. 

 These observations seem to point to the conclusion that it 

 is the central nervous system that is acted upon." Evidently 

 these insects go through a complicated series of actions, 

 the ** dancing " movements of the females incite the males 

 to catch prey and offer it to their desired mates, and the 

 sucking of the victim's juices may stimulate the reproductive 

 functions of the females. 



The act of pairing is followed after a shorter or longer 

 interval by that of egg-laying, in which we see the first, and 

 in the case of many insects, the only manifestation of 

 parental care. Some reference has already been made 

 (pp. 75, 112) to the attraction of various female insects by 

 chemical stimulus to substances suitable for the feeding 

 of their young larvae or nymphs after hatching. A few 

 further examples of the working of this function, extremely 

 important for the life of the race, may be given. 



The dragonflies, already mentioned in this chapter, 

 afford an interesting diversity in the manner of their egg- 

 laying. These insects live during their prolonged pre- 

 paratory stages submerged in the water of ponds and streams, 

 and the majority of females of the order drop their eggs 

 " while flying over the surface of the water, merely by 

 striking the tip of the abdomen from time to time against 

 the water, and so washing off the steady flow of exuding 

 egg-masses " (Tilly ard, 191 7). These masses of eggs are 

 surrounded by a gelatinous substance, which may dissolve 

 in the stream, '' so that the eggs spread out on the river bed." 

 In some cases, however, the effect of the water is to coagulate 

 the gelatinous envelope which may then form a " rope," 

 enclosing hundreds or thousands of eggs, twisted around the 

 twigs of some aquatic plant. The females of the slender 

 ** damsel-flies " (Zygoptera), however, as well as those of the 

 large, elongate Aeschnines, have two pairs of the processes of 

 the ovipositor strongly developed as cutting organs with 

 saw- like edges. By means of these, incisions are made in 

 the stems of reeds or other aquatic plants, and the eggs 



