APODIDyE. 27 



numbers only. Their method of copulation, therefore, is 

 as yet only conjectural. * That one copulation, however, 

 is sufficient for several generations, as in the case of the 

 Daphniae, &c., to be hereafter described, has been ascer- 

 tained. 



SchoefTer tells us that he has carefully isolated the 

 young as soon as born, and found them to produce eggs, 

 from which a second generation was hatched. He also 

 found that the sun and open air were necessary for this 

 purpose, as he has kept them for a length of time in a 

 warm chamber during winter, without their ever hatching 

 their young ; but as soon as warm weather came on, and 

 the vessel which they were in was exposed to the sun and 

 open air, they hatched them in abundance. When taken 

 and placed in a vessel of clear water they may be seen 

 letting their eggs drop from the external ovary to the 

 bottom of the vessel, and in warm weather the young are 

 hatched from the egg in the space of about two or three 

 weeks, f At first they are very different from the parent, 

 undergoing a series of changes before they become fully 

 developed. The egg has two membranes ; one external, 

 coriaceous, the other internal, tender, and pellucid. When 

 it is ripe the external membrane opens at the upper part, 

 showing there a small red body, which may speedily be 

 observed to be in motion. This motion increases, at- 

 tempts seem to be made to burst the internal membrane ; 

 and then, after perhaps half a day, it suddenly leaps out 

 from its envelope, a living animal. The egg then falls to 

 the bottom, and loses its red colour, while the young 

 animal commences forthwith its motion to and fro through 

 the water. At first it is of a rosy colour, and an oblong 



* Zaddach imagines that, he had discovered the male organ. " It consists," 

 he says, " of a small round body near the mesial line on the dorsal part of 

 the last ring of the body, with a small portion on its apex surrounded by an 

 elevated margin." He had traced a nerve running to it. Should Kollar's 

 discovery be confirmed, this statement must "be attributed," to use Bur- 

 meister's words, " to a defective microscopic examination of the organs of 

 generation." 



f Zaddach says twenty days. 



