68 



THE CELL 



themselves out over the object upon which they rest, in large 

 masses about the size of a fist. In order to make a suitable pre- 

 paration for observation of such a plasmodium, it is best to hold 

 a moistened slide near to its edge in an oblique position, and to 

 cause a stream of water by means of a special contrivance to flow 

 slowly down the slide. The plasmodia of the JEthalium possess 

 the property of moving in a direction opposite to that of the 

 stream of water (rheotropism) ; hence they protrude innumerable 

 pseudopodia, and by this means crawl up on to the moistened 

 slide, where they spread themselves out, and, by uniting neigh- 

 bouring pseudopodia together by means of transverse branches, 



they form a delicate transparent net- 

 work (Fig. 39). When this network is 

 examined with a high power, it can be 

 seen to exhibit two kinds of move- 

 ments. 



At first the granular protoplasm 

 which is present in the threads and 

 strands, where it is surrounded by a 

 thin peripheral layer of hyaline proto- 

 plasm, is seen to have a quick, flowing 

 movement, which is chiefly observable 

 because of the movement of the small 

 granules, and w r hich resembles the cir- 

 culation of the blood in the vessels of 

 a living animal. There is no distinct 

 boundary line between the motile endo- 

 plasm and the non-motile ectoplasm, 

 for the granules at the edge of the 

 stream move much more slowly than 

 those in the centre ; indeed, sometimes 

 they may keep quite still for a time, 

 to be later on again caught up by the 

 stream and carried along with it. In 

 the thinner threads there is alwa} 7 s only one stream flowing longi- 

 tudinally, but in the thicker branches there are often two flowing 

 along side by side in opposite directions. " In the flat membrane- 

 like extensions " which are developed here and there in the net- 

 work, " there are generally a large number of branched streams 

 flowing either in the same or in different directions ; not infre- 

 quently we find streams flowing along side by side in opposite 



Fig. 39. Chondrioderma dif- 

 forme (after Strasburger). Part 

 of a fairly old Plasmodium, a Dry 

 spore ; b the same, swollen up in 

 water ; c spore, the contents of 

 which are exuding ; d zoospore ; 

 e amoeboid forms produced by 

 the transformation of zoospores, 

 which are commencing to unite 

 together to form a Plasmodium. 

 (In d and e the nuclei and con- 

 tractile vacuoles may be distin- 

 guished.) 



