io2 ON THE ORIGIN AND [CHAP. 



then swims about freely in the water (PL 5, Fig. 16), 

 thus closely resembling Synura, or one of the Volvo- 

 cineae. After swimming about in this condition for a 

 certain time, the sphere breaks up into the separate 

 cells of which it is composed (PL 5, Fig. 17). As long 

 as the individual cells remained together, they had 

 undergone no changes of form, but after separating 

 they show considerable contractility, and gradually 

 alter their form, until they become undistinguishable 

 from true Amcebse (PL 5, Fig- 18). Finally, according 

 to Haeckel, these amoeboid bodies, after living for a 

 certain time in this condition, return to a state of rest, 

 again contract into a spherical form, and secrete round 

 themselves a structureless envelope. The life history 

 of some other low organisms, as for instance Gre- 

 garina, is of a similar character. 



It may be said, and said truly, that the difference 

 between such beings as these and the Campodea, or 

 Tardigrade, is immense. But if it be considered 

 incredible that even during the long lapse of geolo- 

 gical time such great changes should have taken 

 place as are implied in the belief that there is genetic 

 connection between them and these lower groups, let 

 us consider what happens under our eyes in the 

 development of each one of these little creatures in 

 the proverbially short space of their individual life. 



I will take for instance the first stages, and for the 

 sake of brevity only the first stages, of the life-history 

 of a Tardigrade. 1 As shown in Fig. 60, the egg is at 

 first a round body or cell, with a clear central nucleus 



1 See Kauffmann, Ue^er die Entwickelung und systematische Stel- 

 lung der Tardigraden. Zeits. f. Wiss. Zool. 1851, p. 220. 



