534 



TRANSFORMATION OF ENERGY 



cilia does not take place in one plane. When several cilia co-operate in effecting 

 the forward movement (e. g. Oedogonium and Vaucheria} they must obviously 

 beat at the same rate, otherwise the movements would be quite irregular. 



In addition to natatory movements the lower organisms also exhibit creeping 

 modes of locomotion, necessitating at all events a partial adherence of the body 

 to the substratum. In some cases these movements are due to the exudation 

 of slime from the cells (Desmidiaceae, STAHL, 1880 ; ADERHOLD, 1888 : Oscil- 

 laria, CORRENS, 1897 : and possibly also Diatomaceae, O. MULLER, 1897 : 

 compare also LAUTERBORN, 1896, andScHUir, 1899). Putting on one side such 

 movements as these, which have not as yet been examined in detail from the 

 physiological standpoint, we have left for consideration the locomotory move- 

 ments of naked protoplasmic masses, which creep over the substratum by altera- 

 tions in their form. Such phenomena are spoken of as amoeboid movements, since 

 they were first exactly studied in Amoebae ; in the vegetable kingdom they are 

 exhibited almost solely by the slime Fungi (Myxomycetes). The swarmspore, 

 after escaping from the spore-wall, moves partly in an amoeboid manner partly by 

 means of a flagellum ; later on many of these bodies fuse together into the so-called 

 plasmodium, which continues to exhibit amoeboid movement until the recurrence 

 of the reproductive stage. Owing to its large size, the plasmodium is eminently 



adapted for the study of amoeboid movement, for 

 all the phenomena can often be observed with the 

 naked eye without calling in the services of optical 

 instruments. Such plasmodia, especially those of 

 the Physareae, (Fig. 167), occur on decaying leaves 

 and old tan in the form of much-branched, reticu- 

 late filaments of very varied thickness, the more 

 delicate anastomoses being visible only with the 

 aid of a microscope. DE BARY (1864, p. 37) gives 

 the following account of the general appearance 

 and movements of the plasmodium : ' In one 

 region, the anterior or advancing side of the plas- 

 modium, the chief branches are especially richly 

 subdivided and the terminal twigs are swollen at 

 their ends and spread out in a fanlike manner over 

 the substratum, and united by very numerous ana- 

 stomoses. The individual branches and anastomosing threads of the anterior 

 peripheral network are either thick, hemispherical or circular in section, with 

 club-shaped, swollen and often ragged ends, or they may be flattened out so that 

 the advancing border is thin and perforated, with indented margin and somewhat 

 lobed, the whole being permeated by the stouter branches, like the swollen veins 

 in a mesentery. The plasmodium is soft and slimy in its texture and may be 

 readily smeared out with the finger, and yet it is firm enough to be sectionized 

 with a sharp knife, so as to show the cut edge. Most commonly it adheres firmly 

 to the substratum, but if placed under water large portions separate off, without 

 suffering injury, in soft, elastic but by no means liquid masses.' 



' It may be readily seen with the naked eye that the plasmodium is con- 

 tinuously altering its shape, new branches being pushed out and others gradually 

 retracted, so that the whole body slowly creeps forward.' This may be seen even 

 better, however, under the microscope. ' The chief branches are constantly in- 

 creasing and decreasing in thickness, every here and there broad processes appear 

 on their upper surfaces which slowly or rapidly develop into new branches, while 

 branches already in existence become gradually reduced until they are reabsorbed 

 into the main body. Two branches may be seen growing towards each other, 

 until their ends touch, and the next moment the anastomosis is complete. A 

 lacelike network may thus arise at any point, composed of fine, threadlike uniting 

 strands. If the anastomosis be broken, the two branches are slowly reabsorbed 



Fig. 1 66. Movements of single 

 cilium of a ciliate Infusorian. Alter 

 VERWORN (General Physiology, Jena, 

 1901). 



