THE BEGINNINGS OF LIFE. 487 



apertures in their shell-like envelope. After they have 

 attained a certain size, and after their internal sub- 

 stance has undergone a certain molecular elaboration 

 (of the nature of which we are wholly ignorant), any 

 one of them may quit its cyst and contract into 

 a spheroidal or ovoidal mass, which soon protrudes 

 cilia, and develops into one or other of the numerous 

 varieties of Plassconia or Oxytricha. Whilst, if of 

 smaller size when it quits its cyst, the mass may live 

 for a time as an Amoeba, during which it grows and 

 gradually acquires a sufficient bulk and molecular elabo- 

 ration to enable it to become transformed into one of 

 the above-mentioned Ciliated Infusoria. 



Arcellinx of a similar kind were also seen by 

 Dr. Gros 1 to be produced abundantly from the sub- 

 stance of certain young embryo earth-worms, which had 

 been in his possession (in the egg-state) for more than 

 eighteen months. These Arcellinae, like those produced 

 from the substance of Rotifers, also subsequently gave 

 rise to Ciliated Infusoria, either directly or after a 

 previous amoeboid phase of existence 2 . Whilst, on the 

 other hand, the observations of M. Vogt and M. Nord- 

 mann long ago revealed the fact that bodies resembling 

 Ciliated Infusoria were occasionally budded off from 

 the early embryonic mass of certain of the Gastero- 

 poda. In referring to these observations Dr. Carpenter 



1 Loc. cit., p. 433. 



2 Prof. Agassiz also declares that he has seen Ciliated Infusoria 

 derived from eggs of Planariae (see Appendix D, p. 107). 



