154: THE AMERICAN MONTHLY [July, 



i. MOTOR ORGANS. 



Pseudopodia act as motor organs, for if one of them is protruded 

 from some region of the body of the Amoeba, it may be fixed at its 

 distal end, /*. ^., at the end remote from the x\moeban body, and then the 

 whole of the rest of tliat body can be drawn up to the fixed part. 

 Thus a crude sort of locomotion may be effected. The pseudopodia 

 are at first wholly of ectosarc. After they have been extended for a 

 little while the endosarc flows into the extension of the outer proto- 

 plasm. It is from the numerous changes of form resulting from these 

 extrusions and retractions that the Amoeba takes its name of '• Proteus 

 Animalcule," as Proteus was the shepherd of Neptune, and, much 

 hunted, unfortunate that he was, found it necessary to assume manifold 

 shapes for purposes of disguise. In some Amoebas the pseudopodia 

 are confined to one region of the body of the Amoeba. 



k. REPRODUCTION. 



Only agamogenesis is known positively. The special form of a 

 sexual reproduction that appears to be customary is fission or splitting. 

 One Amoeba is divided into two or more small pieces. Sometimes 

 this division is preceded by encystation, and the Amoeba first surrounds 

 itself with a gelatinous envelope and then splits up. 



/. DEVELOPMENT. 



As this act produces at once a being of the same nature as the parent 

 form nothing can be said under this head. 



in. CLASSIFICATION. 



As Ama;ba feeds on organic things, it belongs to the kingdom 

 ANIMALIA. As it is not made up of two or more cells, it belongs 

 to the sub-kingdom PROTOZOA {jzitioro^ = first, Tw/v = animal). 

 As it has pseudopodia, it is of the class RHIZOPODA (yfn-n- == root, 

 TTo^is- = foot) . As its pseudopodium is broad, it is a member of the 

 order LOBOSA. Genus Avia'ba. 



PRACTICAL WORK AND SUMMARY. 



A. Observe: i. That the body consists of — (a) A central mass of 

 granular protoplasm (endosarc) which extends into some of the pseu- 

 dopodia, and usually contains a nucleus, a contractile vacuole, and food 

 particles. (^). A thin, almost transparent, outer film (ectosarc) 

 which contains few granules. 2. The change in form, appearance and 

 disappearance of pseudopodia, and the movements of the granules. 

 Note that the pseudopodia seems at first to consist only of ectosarc, but 

 that as some of them increase in size the granular endosarc flows into 

 them, and further that a pseudopodium may throw out new processes, 

 and then advance, dragging, and ultimately completely absorbing the 

 body and processes behind it. 



B . Draw an Amoeba at intervals of one or two minutes to show the 

 changes of form, and indicate by arrows the directions of the currents 

 of the granules. 



C. Examine: i. The food particles, note they usually lie at first in 

 a small quantity of water (food vacuole) , and the food may consist of 

 minute plants or animals, and that in addition to food there are often 

 grains of sand and other substances. Studv the process of ingestion 

 of food particles and the expulsion of the non-nutritious particles, and 

 note that they enter or escape from any part of surface. 3. The con- 



