PROTOZOA GREGARIXIDA. 155 



CLASS 3. Gregarinida. 



224. The Gregarinida (Lat. grex, a flock) are internal 

 parasites, infesting the alimentary canal of the cockroach, 

 the earthworm, and other animals. They are destitute of 

 a mouth, and do not protrude pseudopodia. Like other 

 internal parasites, they subsist by imbibing the juices of 

 the animals in which they live. They have the appearance 

 of minute worms, and are sometimes about half an inch 

 long, though generally much smaller. The outer coating 

 is membranous, the interior being filled with sarcode. 

 At one point in the central jelly there is a vesicle, or 

 nucleus, enclosing a solid particle or nucleolus. These 

 are probably reproductive organs. 



225. In certain cases these animals become changed 

 into minute balls, enclosed by a cyst. The nucleus and 

 nucleolus then disappear, and the sarcode is formed into 

 little masses, which are at first round, but afterwards 

 lengthen out, and become pointed at each end. These are 

 called Pseudo-Navicellae (Navicella being a microscopic 

 plant or diatom). The cyst afterwards bursts, and the 

 Pseudo-Navicellze pass out of the body of the animal in 

 which the Gregarinse reside. Some of these are taken 

 into the body of another animal an earthworm, for 

 example ; and then the little mass of sarcode, inclosed 

 within the shell of the Pseudo-Navicella, is set free, and 

 begins to thrust out processes after the manner of an 

 Amoeba. Ultimately, this little animal is developed into 

 a Gregarina like that from which it proceeded. 



