750 MICROSCOPIC FORMS OF ANIMAL LIFE PROTOZOA 



circular row of booklets, closely resembling that which is seen on 

 the head of Teenia. There is here a much more complete differentia- 

 tion between the cell-membrane and its contents than exists either 

 in Actinophrys or in Amoeba ; and in this respect we must look upon 

 (r'regarina as representing a decided advance in organisation. Being 

 nourished upon the juices already prepared for it by the digestive 

 operations of the animal which it infests, it has no need 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 when, as often happens. 



FIG. 582. Cyst of Monocystis agilis, the Gregarinid of the earthworm 

 (750 diams.), showing ripe chlamydospores and complete absence of 

 any residual protoplasm in the cyst. (After Professor Ray Laukester.) 



the cell undergoes duplicative subdivision, the process commences in 

 a constriction and cleavage of this nucleus. The membrane and its 

 contents, except the nucleus, are soluble in acetic acid. The move- 

 ments of the body are of very various kinds ; there is a forward 

 movement which may be due, as suggested by Lankester, to the 

 undulations of the body. The cell itself may undergo contraction, and 

 consequent change in form, which may, or may not. be accompanied 

 by locomotion ; circular constrictions may extend along the body ; 

 or the cell may bend on itself and again straighten out. By Van 

 Beneden the contractility of the cell is localised in a layer of the 



