STRUCTURE OF THE GREGARIN^E. 213 



body, may be divided, just as in the Infusoria, into " a cen- 

 tral column, or medullary parenchyma, a peripheric coating 

 or cortical parenchyma, and a very thin subcuticular coating, 

 which constitutes the muscular coating.'''' 



The medullary parenchyma appears in the greater part of 

 "the length of the cell, under the appearance of a dark band, 

 occupying the axis of the body. It is composed of a very 

 granular substance, and much more fluid than the cortical 

 substance. The grains it contains are rather voluminous, 

 and very refracting ; they are seen to change their places, 

 and move under the influence of the contracticms of the Gre- 

 garinae. The middle parenchyma really constitutes a mas- 

 sive column, which completely fills the hollow cylinder, 

 circumscribed by the cortical parenchyma. The nucleus of 

 the cell, of which the form is usually ellipsoidal, occu- 

 pies the entire breadth of the cylinder. If the body of a 

 Gregarine still alive is cut transversely, either above or below 

 the nucleus, the central fluid matter runs off" in a columnar 

 shape, without carrying away the nucleus with it; and since 

 the cortical matter remains in its place, there develops inside 

 the body a cavity, circumscribed on the outside by the cortical 

 parenchyma, at the top by the nucleus, at the cut end by 

 the exuding medullary column (fig. 6). When the medullary 

 matter spreads, it dilates, the granules separate one from 

 another, and continue diverging, each animated by very 

 intense Brownian movements, each oscillating by itself. 



The cortical layer CLeidy's muscular layer) is composed 

 of a slinly protoplasmic matter, much less fluid, much 

 less granular, and, therefore, clearer than the medullary sub- 

 stance. The granules of the cortical parenchyma are not only 

 less numerous, but much more slender and refracting, than 

 those of the central column. Just as in Infusoria, there is to 

 be found no strong line of demarcation between the two 

 layers ; there is an imperceptible passage from one to the 

 other. Near the posterior extremity of the body these two 

 substances are with difficulty distinguished. The surface of 

 contact between the medidlary parenchyma and the cor- 

 tical parencliyma is not always a simple cylindroid surface ; 

 the medullary coat presents sometimes on the external sur- 

 face channelings approximated more or less one to the other, 

 into which the cortical substance moulds itself. The ridges 

 of the medullary column, and the corresponding sides of the 

 cortical substance, are more or less numerous, and more or 

 kss near to each other. As they are always parallel to the 

 axis of the cylindrical body of the Gregarine, they commu- 

 nicate to it a longitudinal striation, the sides of the cortical 



