96 Protozoa. 



separated. There is almost invariably only a single round nucleus. 

 The Gregarines are mostly elongate ; in many the cell is divided into 

 an anterior smaller^ and a posterior larger, section (the nucleus being 

 in the latter) separated by a thin septum; in others, on the contrary, 

 the cell is quite simple. Sometimes at the anterior end, there is a 

 proboscis-like process which is often armed with hooks, and forms 

 an organ for attachment to the intestinal wall of the host. The 

 Gregarines move about within the host by contraction, expansion, 

 or flexure of the body, movements dependent on the streaming of the 

 protoplasm. Food is absorbed over the whole surface by endosmosis, 

 but no solid material is taken in. 



Reproduction is very characteristic. It begins by the 

 rounding of the body and the secretion of a cyst ; sometimes the 

 actual firm wall of the cyst is surrounded by a gelatinous envelope. 

 This encystation is usually preceded by the conjugation of 

 two individuals, which come into connection without, however, fusing 

 at first ; true fusion only occurs after encysting. A single 

 individual may, however, also encyst. The contents of the cyst divide 

 into a varying number of smaller cells, spores, each of which 

 becomes surrounded with a separate coat. Lastly, the contents of each 

 spore divide to form a small number of most minute cells, usually of 

 elongate form, the falciform young (pseudonavicellEe) . These 

 are liberated by the bursting of the coat ; their further development 

 has not been followed, but it is probable that each develops into a 

 Gregarine. In this group, therefore, reproduction consists essentially 

 in a repeated division of the original cell, usually preceded by 

 conjugation. 



The Gregarines occur as parasites in a large number of Metazoa 

 belonging to the most widely separated groups : Echinoderms, 

 Flatworms, Chsetopods, Arthropods, Molluscs, Vertebrates ; the 

 Myriapoda and Insecta may be mentioned as groups which are 

 specially liable to infection. They occur both in the various cavities 

 of the body {e.g., in the alimentary canal) and also in the tissues. 



Of numerous forms recorded the following may be cited as 

 examples : 



1. Porospora gigantea, very oommon in the alimentary canal of the Lobster, 

 a very long nai-row Gregarine, wMch attains the length (enormotis for a 

 Protozoon) of 16 m/m. 



2. Coccidium oviforme, small ('OSS m/m. long), egg-shaped forms which 

 frequently occur in the bile ducts of the Rabbit, occasionally in Man (where 

 they may cause fatal disease). Whilst young, the Coccidia are naked cells, 

 but later encyst. In this condition they resemble the eggs of certain 

 parasitic worms for which they have been sometimes mistaken. After encysting 

 they pass into the intestine with the bile, and thence escape with the excreta. 

 Development then proceeds to a further stage : the contents of the cyst 

 divide into four spores, within each of which two falciform young develop. 

 If such a spore-containing coccidian cyst is taken in by a i-abbit with its 



