92 PROTOPLASM OF PROTOZOA 



A. terrkola, and of Mast and Doyle (1934) for the ingestion of water 

 by various species of Amoeba in albumin solutions. Penard (1902) has 

 described and figured the pinching off of an extensive injured portion 

 by A. terricola as has Jennings (1906) for A. Umax. The process of 

 egestion, as figured by Howland (1924c) for Amoeba verrucosa, seems 

 also to involve extensive local contraction. 



The lobopodia and filopodia of the Amoebida and Testacea are solid 

 peripherally with a central fluid region, while the pseudopods of the 

 Radiolaria and Heliozoa (axopodia) and those of the Foraminifera 

 (myxopodia) are more fluid peripherally and more solid axially. In 

 axopods and myxopods there can be no flow of endoplasm caused by 

 the elastic contraction of a gelled ectoplasmic cylinder. Roskin (1925) 

 describes the origin of the axopods of Actinosphaerimn by the flowing 

 together and alignment of fibrillae, which eventually fuse into a hollow 

 tube, filled with fluid which is associated with rigidity and contractility. 

 That these axopods do contract rapidly has been shown for Acanthocystis, 

 which, according to Penard (1904), may traverse twenty times its own 

 diameter by rolling along the tips of the axopods, which must adhere, 

 contract, and then release very rapidly. In the foraminiferan Astrorhiza, 

 according to Schultz (1915), pseudopods stretch out five to six times 

 the length of the body, make "feeling" movements and may finally either 

 adhere to the substratum or contract and be withdrawn. The organism is 

 usually fastened by three bundles of pseudopods; if one of these be torn 

 loose, the others contract rapidly and the animal is pulled forward. The 

 axial, more solid stereoplasm of these pseudopodia is distinctly fibrillar. 

 Schmidt ( 1929) has also described the formation of contractile pseudopo- 

 dia in the Foraminiferan Khumbler'inella by the alignment and coales- 

 cence of fibrillae. 



The minute size of cilia and flagella makes it extremely difficult to 

 determine whether their movements are due to active contraction or to 

 changes occurring in the cell which bears them. 



In addition to their usual method of locomotion by means of flagella, 

 many Mastigophora such as the euglenoids show euglenoid movement, or 

 metaboly. In these forms there are present in the pellicle more or less 

 spiral striations, which apparently are elastic in nature and tend to pre- 

 serve the form of the organism during and after the contraction of the 

 superficial layers of the body. In some cryptomonads (e.g., Chroomonas 



