148 COMPARATIVE ANATOMY 



transparent, the contours of the fragment become rounded and 

 irregularly lobed and puckered, and presently it reverts to the 

 slime-like condition, and begins to move, but so slowly that the 

 motion is imperceptible to the eye. In fact, it awakes once 

 more into life. A plasmodium may be of considerable size, 

 covering as much as six square inches, or it may be small, of 

 the size of a sixpence or threepenny bit, but, whether small or 

 large, it shows the same structure. It spreads out over the 

 surface on which it crawls in the form of a network of 

 protoplasm, or rather of a thin sheet of protoplasm traversed 

 by numerous thicker veins of various dimensions which- 

 anastomose with one another, and give the whole a reticulate 

 appearance. In some places the veins are not united by the 

 thin sheet of protoplasm, so that the meshes are empty and a 

 true reticulum is formed. The edges of the plasmodium are 

 usually thickened and puckered in an irregular manner, and 

 occasionally processes of protoplasm, pseudopodia, may be 

 seen to be protruded from them. 



If a small plasmodium is examined under the microscope, 

 for which purpose it can easily be persuaded to crawl over a 

 glass slip, it is seen to consist of protoplasm, the outermost 

 layer of which is clear and transparent, and may be called the 

 ectosarc. The inner mass is opaque and granular, the veins 

 being especially rich in granules. Amongst the granules may 

 be seen particles of inorganic matter, carbonate of lime, and 

 also a large number of round nuclei, each of which has a 

 nucleolus and an achromatic network to which minute 

 chromatin grains are attached. The plasmodium of Badhamia 

 — or any other Mycetozoon — affords an admirable object for 

 studying the characteristic streaming movements of proto- 

 plasm. When watched under the microscope the granules of 

 the endosarc are seen to be in a constant state of movement, 

 streaming first in one direction, then in another. The move- 

 ment is most active in the veins, and is perfectly rhythmical ; 

 the granules stream steadily in one direction for one or two 

 minutes, then slow down and come to rest, and immediately 

 the flow is reversed and they stream back in the direction 

 whence they came. 



The Plasmodium has been described as crawling slowly over 

 the surface on which it lives. This creeping movement appears 

 to be associated with the internal flow of protoplasm, for the 



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