CHAPTER VII. 



SPECIAL MORPHOLOGY AND TAXONOIMY OF THE 

 SARCODINA. 



The term Sarcodina was introduced by Biitschli in honor of 

 Dujardin whose studies on the protoplasm of the Foraminifera led 

 him to believe that the living substance of these forms is simpler 

 than that of other living things and justifying his name for it— 

 sarcode. The peculiarity upon which Dujardin based his con- 

 clusion constitutes the essential difference between these types and 

 other groups of the Protozoa. A definite cell membrane is usually 

 absent and the body protoplasm in general is more fluid and more 

 tenuous than in other t^^^es. In the absence of confining mem- 

 branes and with the play of internal forces, the contour of the body 

 is inconstant or constantly changing a phenomenon expressed by 

 the term amoeboid movement. 



The great majority of Sarcodina are suspended or floating forms 

 (Heliozoa, Radiolaria) and the ground type is homaxonic or spher- 

 ical, but creeping forms are characteristicall\' flattened, while minor 

 variations of the spherical form lead to the greatest variety of radial 

 ellipsoidal and cylindrical types. 



Unlike organisms in the three other great groups of Protozoa 

 the cortex of the Sarcodina rarely shows much structural differ- 

 entiation. In the majority of cases it is soft and highly vesicular 

 but shows a marked tendency to form an outer or inner lifeless 

 mantle of chitin. Such lifeless mantles or membranes may be 

 tightl\' fitting or may be in the nature of tests or houses. They 

 may be of pure chitin as in CocMioy odium, Gromia, etc., or, more 

 frequently, of chitin impregnated with iron oxides, or still more 

 frec{uently may serve as a substratum on which foreign particles 

 or plates and scales manufactured by the organism, are cemented 

 as in the majority of testate rhizopods. Or between lamellae of 

 chitin precipitation of calcium carbonate leads to the formation of 

 the limestone shells of the Foraminifera. Skeletons of silica or 

 strontium sulphate of varied patterns and often of exquisite design 

 are characteristic of the Radiolaria, while spicules, rods and plates 

 of silica are widely distributed amongst Heliozoa and Radiolaria. 



While many of the Sarcodina are t\'pically uninucleate it may be 

 safely stated that this is exceptional in the group as a whole for the 

 vast majority of Mycetozoa, Foraminifera and Radiolaria are 

 multinucleate. Nuclear dimorphism, however, does not occur and 

 the multinucleate condition is brought about bj^ fusion of cells to 



