GENERAL MORPHOLOGY 21 



colony is a more perfect compound individual in which the cells are 

 embedded and held together in a common gelatinous matrix (Fig. 3). 

 An arboroid colony is one formed by continuous division of cells 

 which remain attached at some point, such colonies often being large 

 dendritic branched aggregates (dinobryon, epistylis, carchesium, etc., 

 Fig. 4). A catenoid colony, finally, is formed by the union of two or 

 more cells end to end or side by side. 



(a) Protoplasmic Structure. — The body of a protozoon is made 

 up of a somewhat gelatinous, diaphanous substance, to which Dujar- 

 din, in 1835, gave the name "sarcode," but which M. Schultze, in 1S63, 

 showed to be identical with the substance "protoplasm" of higher 

 plants and animals, and named by von Mohl in 1846. The minute 

 structure of this protozoon protoplasm appears to be little more than 

 a fine network, the meshes of which are sometimes minute and narrow, 

 as though compressed, and sometimes large and open. The substance 

 of the walls of the meshwork appears to differ noticeably from that 

 within its spaces, the former more dense and made up of fine granules 

 (microsomes), the latter more fluid and containing granules of con- 

 siderable size. Microchemical reactions show that these granules 

 differ in chemical composition, and that some are reserve food par- 

 ticles, others reserve matters for one use or other, and that still others 

 are waste matters. This protoplasmic make-up, which Biitschli ('92) 

 compared with a foam structure (Schaumplasma), was described by 

 him as consisting of fine drops of a liquid alveolar substance, enclosed 

 within the meshes of a continuous interalveolar substance, also liquid 

 but of a different density. Each alveolus he compared with a bubble 

 in a foam structure; the air of the bubble corresponding to the alveolar, 

 the walls to interalveolar, substance. 



While the inner protoplasm of all protozoa is probably alveolar in 

 nature, there is considerable variation in structure due to the great 

 variations in size of the alveoli and of the granules contained within 

 them. In some forms {e. g., in the heliozoon actinospherium) the 

 vacuoles are so large as to give a parenchymatous appearance to the 

 cell, but in others they are so minute as to give a uniformly dense 

 appearance; between these two typical cases fall the remainder of the 

 types of protozoa. The granules within the walls of the alveoli are 

 equally variable in size; in some cases they are very minute, corre- 

 sponding, apparently, to the fine elementary granules which Altmann 

 ('94) regarded as the basis of all protoplasm, while in other cases they 

 are obviously of different kinds. There is reason to believe that some 

 of these interalveolar granules are endowed with a specific function, 

 and that some of them underlie the various motor activities of the cell 

 ("kinoplasm" of Strasburger; "ergastoplasm"' of Prenant). It is 

 certain that the protoplasmic alveoli tend to condense toward the 

 periphery of the cell, the condensation due, apparently, to the loss of 



