PROTOZOA : GREGARINID^:. 



45 



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 ex- 

 cretion must be performed simply by the general surface of the 

 body. The body is, nevertheless, contractile, and slow move- 

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



In spite of their exceedingly simple structure, the following 

 very interesting reproductive phenomena have been observed, 



Fig. i. Gregarina of the earth-worm, a Adult Gregarina ; b The same encysted ; 

 c With the contents divided into pseudonavicellae ; d Free pseudonavicellae ; 

 e Free amoebiform contents of the pseudonavicellae. (After Lieberkiihn.) 



sometimes in a single Gregarina without apparent cause, 

 sometimes as the result of the apposition and coalescence of 

 two individuals the exact nature of the process being in 

 either case obscure. The Gregarina or it may be two in- 

 dividuals which have come into contact and adhered together 

 assumes a globular form, becomes motionless, and develops 

 round itself a structureless envelope or cyst, when it is said 

 to be "encysted" (fig. i, b\ The central nucleus then dis- 

 appears, apparently by dissolution, whereupon the granular 

 contents of the cyst break up into a number of little rounded 

 masses, which gradually elongate and become lanceolate, when 

 they are termed "pseudonavicellae" (or " pseudonaviculae ") 

 (fig. i, c). The next step in the process consists in the libera- 

 tion of the pseudonavicellae, which escape by the rupture of 

 the enclosing cyst (fig. i, d). If they now rind a congenial 

 habitat, they give origin to little albuminous or sarcodic 

 masses, which exhibit lively movements, and are endowed 

 with the power of throwing out and retracting little processes 

 of the body which closely resemble the " pseudopodia " of the 

 Rhizopoda; so that the pseudonavicella in this condition is 

 very similar to an adult Amoeba (fig. i, e). Finally, these 



