182 The Structure of Protoplasm 



slightly gelated protoplasm of the pseudopods solates and joins the 

 endoplasm. The endoplasm is also enhanced by solation along the 

 borders of these small streams. The solation and backward flow 

 continues until the tips are weakened and the contractile tension 

 becomes less than that which develops at the posterior end. The 

 flow is then reversed, and the cycle is repeated. 



There are a number of important differences between the anterior 

 end and the posterior end. The small plasmolets with a single pos- 

 terior end and one main tube about 100 microns in diameter may 

 have a dozen lobes at the anterior end with one to four pseudopodia 

 on each one. The main tube branches and rebranches in the broad 

 zone into about forty more or less temporary little terminal chan- 

 nels which supply approximately a corresponding number of pseudo- 

 podia. Some lobes enlarge, subdivide, and spread more than others. 

 The channels leading into such lobes increase in size as do also the 

 number of branches and the number of terminal channels. Some 

 lobes decrease in size and become retracting ends, and a reverse 

 series of events occurs until finally through contraction and solation 

 all traces of the lobe are lost. The whole response of the branching 

 system of channels and terminals to enlarging areas reminds one of 

 the growth of capillaries and the formation of veins and arteries in 

 growing regions of the vertebrate embryo. A fantastic comparison 

 can be made of the functional response of the tubes and channels of 

 the slime mold with the developing vascular system of man. 



MICROSCOPIC STRUCTURE OF SLIME MOLD 



The visible microscopic structure of the slime mold seems to be 

 somewhat similar to that of the ameba as described by Mast (1926) . 

 The thin areas of the transition zone can be examined with the oil 

 immersion lens, and Camp (1937) took advantage of them for his 

 observations on the minute structure of the protoplasm. His descrip- 

 tion which I now quote can be readily confirmed (p. 316) : ''The 

 protoplasm. Careful microscopic examination of very thin areas of 

 a plasmodial sheet reveals the presence of an optically homogeneous 

 substance which has an exceedingly faint bluish-gray color. This 

 is the substance which is generally recognized and referred to as 

 hyaloplasm. Scattered throughout the hyaloplasm there are numer- 

 ous granules, vacuoles, and particles of ingested material. The 

 granular bodies exhibit widely varying degrees of optical differen- 

 tiation, and they vary in size from approximately 0.2 microns to 

 slightly more than 1 micron. In general they are more or less 



