48 Structure and Classification of Micro-organisms 



form, but there may be adaptations, such as an oral aperture, some- 

 times infundibular in shape and communicating with the soft 

 endosarc through a blind tube. An anal aperture may also be 

 present. 



In the higher infusoria the ectosarc may also be continued pos- 

 teriorly to form a stalk, by which the organism attaches itself 

 (Vorticella) . Such stalks are contractile. 



Nucleus. — In certain protozoa of very simple and indefinite 

 structure — spirochaeta and treponema — no distinct well-contoured 

 nucleus can be observed. 



In the rhizppoda the nucleus is a distinct organ surrounded by a 

 nuclear membrane and containing the usual chromatin and linin. 



The greater number of mastigophora possess two distinct bodies, 

 either a nucleus and a centrosome or a major and minor nucleus. 

 This is well shown in trypanosoma. 



The infusoria vary greatly in the character of the nuclei. As a 

 rule, there are two indefinite nuclei, the macronucleus and the 

 micronucleus. Both seem to be essential organs, and in the phe- 

 nomena supervening upon conjugation both participate. The 

 nuclei of the protozoa are, therefore, extremely diversified, and 

 vary from the most simple collections of granules of nuclear sub- 

 stance to large well-formed fantastically shaped composite organs. 



Movement. — Some kind of movement is to be observed at some 

 period in the life of almost every protozoan. 



In rhizopoda with the soft ectosarc the movement consists of 

 flowing currents by which lobose projections of the body substance 

 appear now here, now there, in the form of pseudopodia, or else a 

 continuous flowing, by which the upper surface continually coming 

 forward in a thin layer coincides with the progress of the animal, 

 which continually rolls over and over as it were. 



In mastigophora the movement of the more rigid bodies is effected 

 through the presence of longer or shorter, flexile or rigid, coarse 

 threads or "whips." These usually project anteriorly — trypano- 

 soma — and by means of a spiral movement draw the cell along with 

 a propeller-like action; symmetrically arranged flagella may operate 

 more like oars. 



The sporozoa usually manifest very little movement, yet their 

 sporozoites are motile, and the spermatozoites are also motile and 

 commonly flagellated. 



The infusoria are actively motile through abundant fine hair-like 

 formations known as cilia. These, multitudinous as they are, 

 vibrate synchronously with an oar-like movement, propelling the 

 organisms forward or backward or making them revolve with great 

 rapidity. Independent cilia not infrequently encircle the oral 

 aperture, causing a vortex, in which the minute structures upon 

 which the creatures feed are caught and carried into the body. 



Size. — The protozoa show very great variation in size. Some of 



