448 



PROTOZOA : GREGARINA. 



between the cell-membrane and its contents, than exists either in 

 Aetinophrys or in Amoeba; and in this respect we must look 

 upon Gregarina as representing a decided advance in organization. 

 Being nourished upon the juices already prepared for it by the 

 digestive operations of the animal which it infests, it has no need 



Fig. 236. 



Gregarina of the Earthworm :— a, in its ordinary aspect ; b, in 

 its encysted condition; c, d, showing division of its contents 

 into Pse\ido-navicellre ; e, f, free Pseudo-navicelhe ; h, free 

 Amceboids produced from them. 



of any such apparatus for the introduction of solid particles into 

 the interior of its body, as is provided in the 'pseudopodia' of the 

 Rhizopods and in the oral cilia of the Infusoria. Within the cavity 

 of the cell, whose contents are usually milk* white and minutely 

 granular, there is generally seen a pellucid Nucleus ; and this 

 becomes first constricted and then cleft, when, as often happens, 

 the cell subdivides into two, by a process exactly analogous to that 

 which takes-place in the simplest Protophytes (§ 185). The 

 membrane and its contents, except the nucleus, are soluble in 



