426 SECOND PART.—MYCETOZOA. 
eye. The microscope reveals a constant change of outline in all the branches, some- 
times in the form of a slight undulating movement, sometimes of an unceasing 
protrusion and withdrawal of small pointed tentacle-like processes or pseudopodia. 
Some of these pseudopodia or single flat projections of the main branches swell into 
a knob at the free extremity and presently grow into larger branches, while in another 
part branches diminish in size and gradually sink back into the main stem. Here 
two branches grow out towards each other till they touch one another, and then 
coalesce and anastomose; there a branch becomes constricted at some point and 
divides into two. By these processes a plasmodium may separate into several parts, 
and several plasmodia may be united into one; but according to Cienkowski’s and 
my own observations union never takes place between plasmodia of different species. 
Branches of every degree and every size participate in the movements, and the smaller 
the branch the more active is its movement. The alternation in the movements 
takes place at all points alike in the plasmodium, but the protrusion of branches 
predominates on one side, the retraction on the opposite. Hence there is often an 
active advancing movement, a locomotion of the plasmodium in the direction of the 
greater protrusion, and the anterior portion of the whole body which leads the way 
in the advance assumes the form of a system of branches with swollen extremities, 
which spread out like a fan and are connected together into a reticulated structure 
by numerous and constantly changing anastomoses; in other words it becomes a 
flat surface pierced so as to form a sieve or net and traversed by the stronger 
branches like swollen veins, its margin being thickened and uneven (Fig. 185). 
The inner substance of the plasmodium is also subject to a variety of active 
movements and displacements which are seen to be directly connected with the 
amoeboid movements, but sometimes appear to be independent of them. First there 
are the previously mentioned swellings and sinkings of the marginal hyaloplasm, the 
locality of which is constantly changing. Secondly stream-like displacements of the 
inner granular plasm with change of speed and direction. The varying breadth of 
‘the marginal hyaloplasm shows that there is a constantly varying pressure of the 
granular mass in the direction of the periphery. The movement in the interior takes 
place in the form of streams which occupy the whole breadth of a branch, or run in 
narrow threads through the surrounding substance which is apparently motionless. 
The movements are chiefly directed towards the swelling and advancing extremities 
of the branches, into which the granular mass streams in, the alternating backward 
flow being weaker and less copious. The reverse takes place in branches which are 
being withdrawn. But movement and streaming may be constantly alternating with 
rest in the interior of the plasmodium without this prevailing and directly perceptible 
connection with the amoeboid change of shape. 
Further details with respect to these phenomena must be sought in monographs 
and in the physiological treatises which have appeared since my first work on this 
subject. See also below in section CXXVII. 
The surface of the plasmodia of the Physareae which I have examined is 
covered with a soft shiny envelope, which is not distinctly defined on the outside but 
_ is quite distinguishable from the marginal layer. It forms a border round the thicker 
branches which is often more than 0,01 mm. in thickness, and is in itself colourless 
and pellucid but is often covered with small particles of soil which adhere to it. 
