1!'-^] A'pise/.- Amoebae of Culture Rats and Mice 501 



describe a third outer layer, the hyaloplasm, as is found in some 

 amoebae (see Schaeifer, 1920). While it appears at times that there 

 are two layers outside the endoplasm, a thin, clear outer layer and an 

 alveolar middle layer, these two layers blend so, one into the other, 

 that, as a rule, the line of demarcation is indistinguishable. These two 

 layers will therefore be described as constituting the ectoplasm. In 

 stained slides the ectoplasm appears to be finely alveolar in structure. 



The great activitj' with which the amoebae move forward, the 

 remarkable coordination during the progressive movement, the sudden- 

 ness with which pseudopodia are formed, the contractility exhibited 

 by the protoplasm, and the indescribable contortions indulged in by 

 the active amoebae, lead one to disregard the earlier theories, which 

 endeavored to explain amoeboid movement as the result of surface 

 tension, and to conclude with Sehaeffer (1921) that the mechanism 

 controlling locomotion and movement is primarily internal rather than 

 that the pseudopodia move the amoeba. 



The endoplasm contains the nucleus and the numerous vacuoles, 

 some containing undigested food and some being filled with liquid. 

 The endoplasm which surrounds these structures presents a flaky 

 appearance similar to that of the cytoplasm which is found in the 

 encysted stages. No contractile vacuole has been observed at any time. 



Size. — Grassi (1881) described the average size of the motile 

 amoebae a.s 13.2jn. Wenyon (1907), however, recorded the motile forms 

 as mea.suring from 30-40/t. Rudovsky (1921) figured motile forms 

 measuring 30/t in diameter. The rounded motile forms, measured on 

 permanently stained slides in this investigation, average 19fi. With 

 extended pseudopodia, the length is greatly increased, forms 40;u in 

 length and SOju in breadth having been encountered. An attempt to 

 determine racial differences in size within the species, from the motile 

 forms, such as is very evident among the cysts, indicates that there 

 is a corresponding racial difference in the motile forms, the average 

 diameter of the largest race in this phase being 21.5/^ while the 

 average of the smallest is IS.ljtt. The cysts of these races average 

 respectively 17.7/a and 14.5/i. This affords an approximate ratio of 

 the volume of rounded unencysted amoeba to the cyst as 1.2 is to 1 ; i.e., 

 the volume of the rounded motile amoeba is 0.2 greater than the 

 corresponding cyst which it forms. 



}fuclei. — The nuclei of free forms of Councilmania nniris are dis- 

 tinguishable from the food vacuoles in normal saline solution by a 

 more opaque appearance and by a darker gray color. In the iodine- 



