439 



as looo ova but only 60 or 70 of them were of normal size and con- 

 sidered mature. Another female, Ischnura verticalis, contained 203 

 mature ova, while a third teneral female of Bnallagnm hageni con- 

 tained 290 mature ova. Calvert ('93) says that the average dragon- 

 fly probably lays between two and three hundred eggs, and this state- 

 ment seems to coincide with that above. 



The length of time spent in the egg stage is also imperfectly 

 known. Lucas ('00: 18) reports that Sympctruin striolatum spends a 

 month in this stage. Balfour-Browne ('09:256) says that eggs of 

 Ischnura clcgans and Bnallagma pidchclhmi, laid at the beginning of 

 August at East Norfolk, England, required from four to five weeks 

 to develop. The temperature relations are not mentioned, but it is 

 probable that this period varies to some extent. Needham ('03) calls 

 attention to the fact that the eggs of Lestes, which are laid above 

 water late in July, develop to a certain point, apparently ready to hatch, 

 and await submergence before eclosion. The water does not reach 

 them until late in fall ; and this means that at least several months are 

 spent in the egg stage. Brandt ('69) reported the development of 

 Agrion (Caloptcryx) znrgo in three weeks during a hot summer. 



In the final stages of embryonic development the head is directed 

 towards the small end of the egg. This end is always nearest the 

 cuticle of the plant, and the nymph consequently emerges head first. 



NYMPH 



Grozvth. — Immediately after hatching, the nymph is helpless and 

 unable to move about actively. In this condition it is known as the 

 pronymph (Balfour-Browne, '09:258). A few minutes afterward the 

 skin of the pronymph splits and the true nymph escapes. During the 

 second nymphal stage the nymph is a minute insect, hardly longer than 

 the egg from which it hatched. The antennal segments are three 

 and there are no wings or sexual appendages. From this stage the 

 nymph grows and molts at intervals, the time between molts depending 

 largely upon the temperature and the amount of food which it is able 

 to capture. The antennae increase in number of segments until six 

 are present, in which condition they remain until the last nymphal 

 stage, when there are seven. The wings appear as ridges during the 

 fourth stage, but the sexual appendages do not appear until the seventh 

 stage, according to Balfour-Browne ('09). This seems to be contra- 

 dicted by the rather frequent observance of nymphs without wing-cases 

 and fairly well-developed appendages. There is great variation in the 

 time between molts, due primarily to temperature. It often happens 



