The Protozoa 55 



The body substance may show no morphologic differen- 

 tiation in rhizopoda, but in the corticata there may not only 

 be a permanent form, but there may be adaptations, such as an 

 oral aperture, sometimes infundibular in shape and communi- 

 cating 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 

 posteriorly 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 rhizopoda 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 phenomena supervening upon conjugation both par- 

 ticipate. The nuclei of the protozoa are, therefore, extremely 

 diversified, and vary from the most simple collections of 

 granules of nuclear substance to large well-formed fantastic- 

 ally 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 pseudo- 

 podia, 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 presence of longer or shorter flexile or 

 rigid coarse threads or " whips." These usually project an- 

 teriorly trypanosoma and by means of a spiral move- 

 ment draw the cell along with a propeller-like action; sym- 

 metrically arranged flagella may operate more like oars. 



The sporozoa usually manifest very little movement, yet 

 their sporozoites are motile, and the spermatozoits are also 

 motile and commonly flagellated. 



