PROTOZOA : GREGARINIDA. 59 



however, has been founded upon individuals of this kind, under 

 the name of Dicystidea;, the name Monocystidea being retained 

 for the ordinary forms. As regards the size of the Gregarince, 

 they vary from about the size of the head of a small pin up 

 to as much as half an inch in length, when they assume the 

 aspect of small worms. The integument or cuticle with which 

 the protoplasmic body is enclosed may be quite smooth or 

 striated, or it may be furnished with bristles or spines, or even 

 in some cases with cilia. Sometimes one end of the body is 

 furnished with uncinate processes, very similar in appearance 

 to the hooked "head" of the common tape-worm (Tania 

 soliuni). Essentially, however, the structure of all appears to 

 be the same. No differentiated organs of any 'kind beyond 

 the nucleus and nucleolus exist, and both assimilation and 

 excretion must be performed simply by the general surface of 

 the body. The body is, nevertheless, contractile, and slow 



,. encysted; d Further stage 



same, with the contents divided into " pseudonavicellae ; " e Free " pseudonavi- 

 cellse ;" / Amoebiform mass of protoplasm liberated from a pseudonavicella ; g and 

 h Active forms ofy". All the figures are greatly enlarged. 



movements can be effected, not, however, by pseudopodia. 

 Hasckel regards the Gregarinff, as Amcebce which have become 

 degenerate by parasitism ; but this opinion is rejected by Van 

 Beneden, and their apparently unicellular structure would 



