210 FRESH-WATER EH1ZOPODS OF NORTH AMERICA. 



are produced from certain of the plates, and seem to be a highly developed 

 condition of the minute point at the upper median portion of the plates of 

 the shell generally. The plates of the shell have considerable thickness, 

 and appear to be lenticular or doubly convex. Those surrounding the 

 mouth and forming its dentated border are usually conspicuously thicker 

 than the rest. 



In several instances, in some specimens, it has appeared to me that the 

 second row of plates, above the oral series, was denticulated in a similar 

 manner with these, as represented in fig. 18. 



The sarcode of JEughjplia alveolata and of other species does not differ 

 essentially from that of the Difflugian forms. It usually occupies nearly 

 the whole or the greater part of the interior of the shell. It almost invaria- 

 bly extends to the fundus, no matter what may be its reduction laterally or 

 contraction from the sides of the shell. It is frequently more or less con- 

 stricted in a somewhat hour-glass manner ; but I never observed it adherent 

 to the inner part of the shell by pseudopodal threads, as is so commonly 

 the case in the Lobose Protoplasts. 



Usually the sarcode is colorless, or is mainly so; though, from the 

 admixture of food, it may appear to a variable extent yellowish or brownish, 

 with darker colored spots, commcnly green, from the presence of algae. 

 The basis of structure is a pale and finely granular protoplasm, and 

 included in this are the usual elements found in most other Protoplasts. 

 A large clear nucleus occupies the fundus of the sarcode mass, containing 

 a pale granular central nucleolus, mostly obscurely or not at all visible 

 without the action of acetic acid or other agent. Below the position of the 

 nucleus, and partially enveloping it, a broad zone of the sarcode is mingled 

 with an abundance of minute oil molecules, which give to this portion of 

 the animal, when viewed by reflected light, a milk-white appearance, but 

 by transmitted light a more or less black and punctated appearance. 



Between the zone of oil molecules just indicated and the mouth of 

 the shell, the sarcode often presents variable proportions of mingled food, 

 sometimes as diffused and colored granular matter, and sometimes as 

 colored granular balls included in drops of colorless liquid. Food 

 materials of a more distinct character, as diatoms and other alga?, are also 

 often seen in this position. Clear liquid globules in variable proportions 

 and sizes are likewise frequently seen mingled with the foregoing. Con- 



