296 THE BEGINNINGS OF LIFE. 



never seen a preliminary coupling of two individuals. 

 In specimens of the genus Kerona he has occasionally 

 observed this coupling, though he has never seen more 

 than a single germ. The nature of the body in these 

 animals was rendered even more indubitable by the fact 

 that it became converted into an embryo whilst still 

 within the posterior part of the body of the parent. 

 His observations were principally conducted upon spe- 

 cimens of Kerona lepus measuring -3-^-" in diameter, 

 and in which the germ (here again free within the body) 

 was about 11 1 00 // in diameter. M. Pouchet saw a gyra- 

 tion of the embryo, and the characteristic contractile 

 vesicle make its appearance, so as to leave no doubt 

 that the process of development was still advancing \ 

 Multiplication by the ordinary processes of repro- 



1 This production of embryos in the substance of dying Infusoria is 

 a subject of much interest. To me it was a matter of special interest to 

 read (in 1869) M. Pouchet's description after I had already, as a result 

 of frequent careful observation, come to the conclusion that the nucleus 

 of the white blood corpuscle was also evolved during the later stages 

 of its life within its very substance ; and that it was destined to come to 

 maturity and perhaps, under certain circumstances, take the form of a 

 distinct anatomical element, whilst the rest of the parent structure was 

 about to undergo a process of disintegration (see' vol. i. p. 227). This 

 process seems to be most comparable with that by which the embryo 

 is evolved within the body of the Infusorial animalcule. Here also the 

 germ (nucleus) is evolved out of the substance of the parent organism 

 itself, at a time when its own vitality is about to cease. As a sort of 

 link connecting these two sets of phenomena, we may perhaps refer to the 

 development of the moving filaments known as Spermatozoa from the 

 nucleus of the sperm cell. The old element dies in giving birth to the 

 new product ; and the new element in this case is an actively-moving, 

 independent zooid. 



