GENUS AMCEBA— AMCEBA PROTEUS. 41 



Independently of the food-balls, which ordinarily are formed from soft 

 and readily yielding materials, the endosarc is often observed to contain 

 other food of a more consistent character, greatly differing in the size 

 of the morsels and frequently more or less readily recognizable from their 

 form. Such materials cornmonty consist of the various diatoms, desmids, 

 green unicellular alga?, and zoospores of the filamentous alga3. Consid- 

 erable fragments of the latter, such as Oscillaria, Zygnema, etc., are also 

 often seen among the food contents. Occasionally animal forms may 

 be detected in the food materials of the endosarc, among the most com- 

 mon of which are the Rotifers, and in several instances I have observed 

 with them an unfortunate Arcella, a Difflugia, or a Trinema. 



These more consistent and persistent food materials, like the food-balls, 

 are often observed included in water-drops swallowed with the food, but 

 they also frequently appear without any such liquid investment. 



Other materials related with the food, and frequently forming part of 

 the endosarc-jumble, consist of fragments of various vegetal tissues, such 

 as portions of cellular tissue of macerated leaves, vessels, ligneous fibres, 

 and hairs. In some fine large vigorous specimens of Amoeba proteus col- 

 lected from a pond in the vicinity of a saw-mill, the endosarc contained 

 multitudes of particles of sawdust. 



In addition to the food materials and other elements of the endosarc 

 of Amoeba proteus, it frequently contains variable proportions of quartz- 

 sand in irregular angular particles. 



G. A remarkable and pretty constant element of the endosarc, appa- 

 rently of an intrinsic character, consists of minute crystals, as seen in fig. 

 1 1 , pi. II. They have been observed in this and other Rhizopods by many 

 investigators. Though very evident, I have generally failed to determine 

 their exact form or the system to which they belong. 



7. An important element of the endosarc is the nucleus, seen in most 

 of the figures of pis. I and II. It usually occupies a position posterior 

 to the middle of the body, but may be shifted to almost any other position 

 in the movements of the animal. Mostly it appears as a rather conspicuous 

 compressed spheroidal, or thick discoid body, with the broad surfaces some- 

 what convex, flat, or slightly depressed, and the border rounded. It is often 

 surrounded by a clear halo, apparently consisting of a globular envelope of 

 clear protoplasm. Tn different Amoeba? of various sizes, and from dif- 



