28 



INVERTEBRATE ANIMALS. 



In anatomical structure a Gregarina usually presents the 

 appearance of a single cell, consisting of an ill-defined mem- 

 branous envelope, filled with a more or less granular sarcode 

 containing fatty granules, and having in it a little central 

 bladder or vesicle the " nucleus " which in turn encloses a 

 solid particle or " riucleolus " (Fig. 2, a). The outer covering 



FIG. 2. Anatomy and reproduction of the Gregarina of the earthworm (after Lieberkiihn). 

 a Adult Gregarina ; b The same " encysted ; " c With the contents broken up into 

 pseudonavicelloe ; d Free pseudonayicellae; e Contents of the pseudonavicellse when lib- 

 erated. 



or cuticle with which the protoplasmic body is enclosed may 

 be quite smooth, or it may be furnished with bristles or 

 spines, and in some cases even cilia have been observed. Be- 

 yond the nucleus and nucleolus (which are probably connected 

 with reproduction), no definite organs have been detected in 

 the Gregarince ; and all the processes of assimilating food 

 and getting rid of waste or injurious products must be effected 

 by the general surface of the body. As we shall see, how- 

 ever, this is common in internal parasites, which are not 

 necessitated to live upon solid food, but which are enabled to 

 subsist simply by imbibing the nutritive juices of their hosts. 



The following is a brief outline of the process of reproduction as it has 

 been observed in the Gregarince, sometimes in a single individual, some- 

 times in two individuals which have come together and completely coalesced 

 and melted into one another. The Gregarina becomes completely motion- 

 less, assumes a globular form, and develops round itself a thick structureless 

 coat or envelope, when it is said to be " encysted " (Fig. 2, b). The nucleus 

 then disappears, and the sarcode of the body breaks up into little masses, 

 which are at first rounded, but afterward become pointed at both ends, when 

 they are called " pseudonavicellae " (Fig. 2, c). The cyst then breaks and 

 the pseudonaviceliae escape, when they give origin to little masses of sar- 

 code, which have the power of active movement and of throwing out pseudo- 

 podia, thus coming closely to resemble the animalcule which will be directly 

 described as the Amceba (Fig. 2, e}. These little amoeba-like masses, if they 

 find a suitable locality, are finally developed into new Grcgarince. 



