THE MYCETOZOA 45 



spaces between the thickenings. Hence in these regions the plas- 

 modium consists of a reticulum of anastomosing branches, extended 

 over the substratum. The arrangement of the branches closely 

 resembles that of the vessels traversing the mesentery of a mammal, 

 and, before their relation to the spore-bearing stage of the life- 

 history was known, the name Mesenterica was, in fact, given to- 

 plasmodia of certain forms, under the supposition that they repre- 

 sented a new genus of fungi. 



The form and degree of concentration of the plasmodium 

 vary widely according to circumstances. Sometimes it is 

 aggregated in a thick layer on the surface, as after emerging from 

 the interstices of a mass of rotten wood or tan, at other times it 

 is widely expanded in a thin layer of exquisite delicacy. Fries 

 relates how the plasmodium of Diachaea elegans which he had 

 laid in his hat, while collecting, spread within an hour over a 

 great part of the latter in an elegant white network. 



By suitable manipulation the plasmodia may readily be induced 

 to spread over glass cover-slips, and may thus be examined micro- 

 scopically. 1 When thus seen the vessel-like thickenings are found 

 to be, in fact, streams of moving protoplasm. The flow may be 

 traced from the larger branches through the smaller into the 

 advancing border of the plasmodium, which becomes swollen and 

 more opaque as the streams pass into it. After a short time the 

 current is seen to slacken, then to stop, and shortly to begin again 

 in the reverse direction, the margin becoming thinner and more 

 transparent as the protoplasm leaves it. In a short time the flow 

 is again reversed, and again directed to the advancing border. 

 Thus a rhythmic flow, towards the margin and away from it, is 

 kept up through the plasmodium the period in each case being, 

 in healthy conditions, about a minute and a half to two minutes,, 

 though its duration is always longer in the direction in which the 

 plasmodium is moving than in the other. 



The plasmodium is invested by a thin layer of homogeneous 

 hyaline and colourless protoplasm. Within this the protoplasm is 

 highly granular. 



The hyaline layer is exceedingly thin over the greater part of 

 the periphery, but at the advancing border it is of considerable 

 breadth. The advance over the substratum occurs chiefly while 

 the flow in the veins is directed towards this border. Under 

 these circumstances the border becomes more and more turgid, and 



1 An easy way of making microscopic preparations of living plasmodia is to lay 

 out a number of cover-slips on a plate, sprinkle them with rain-water, and then to 

 scatter small fragments of sclerotium over them. In a moist atmosphere the 

 encysted protoplasm resumes the active stage in the course of a few hours, and the 

 small plasmodia thus arising spread in delicate fan-like expansions over the glass. 

 The cover-slips may then be mounted over a hole in wet blotting-paper, on a slide, or 

 in some other manner, ensuring the maintenance of a moist atmosphere. 



