190 PHILIP P. CALVERT. 



enables the water to wash the eggs from her body. While the eggs 

 are usually distributed in small numbers, Gerard found bunches of 

 30-40 egg-masses, each twelve to fifteen inches long and one-eighth 

 of an inch in diameter, with about 500 eggs to the inch, and which 

 subsequently yielded Libelluline larvae (Am. Ent. iii, pp. 174-75). 

 While the male usually releases his hold of the female immediately 

 after copulation, Dlplax frequently oviposits in pairs. Even when 

 the male separates, he frequently follows the female while she is 

 discharging the eggs. 



Most individuals probably pair more than once. A second pairing 

 may take place while a female is in the very act of oviposition, as 

 the writer has observed in Plathemis trhnacu.lata and LiheUula pul- 

 chella; in both of these cases, after the interruption, the female re- 

 sumed the discharge of the eggs. 



2. Devklopment of the Odonata. 



EMBRYONIC (oval) DEVELOPMENT. 



The eggs of the Odonata are smooth, |)ale yellow, elongated in the 

 endophytic, elliptical and wider in the exophytic forms. The period 

 of oval development varies from six days in LiheUula pulchella and 

 Ischnura verticalis, to three weeks in Calopteryx virgo (Brandt). The 

 number of eggs laid by one female is very variable ; 800 was the 

 highest found by Brandt in C. virgo. 



Our knowledge of the embryonic development of the Odonata is 

 based chiefly on the researches of Brandt (18) on Calopteryx virgo. 

 What is here presented is mainly an abstract of his paper. 



The anterior pole of the freshly-laid egg is distinctly more pointed 

 than the posterior. An examination of the outline of the egg shows 

 (me of its long sides to be almost straight, while its opposite side 

 is distinctly convex ; the straight side corresponds to the ventral 

 surface of late, but not early, embryonic life, and the convex side 

 to the dorsal surface of late embryonic life, and will be so desig- 

 nated in the following account. The length of the egg is 1 mm,, 

 its greatest breadth .2 mm. Two membranes enclose the egg, an 

 outer (chorion) and an inner (vitelline membrane). The chorion is 

 structureless and at first colorless; it is thickened at the anterior 

 pole, and here also a small gelatinous mass adheres. The micropyle 

 passes excentrically through the summit of this thickening of the 

 chorion. Moreover, a delicate, folded, funnel-like membrane is 



