532 GENERAL CONSIDERATION OF PROTOZOA 



of this type are certain white blood corpuscles, or leukocytes. Just 

 as these can send out pseudopodia, crawl around in the tissues and 

 engulf and digest bacteria, so certain protozoa known as amebce exhibit 

 exactly the same phenomena. A distinction is made between lobopodia 

 which are the digit-like, irregular, soft, and inconstant pseudopodia, 

 and filopodia, which are more stiff, less motile, and quite permanent. 

 They are often distributed more or less regularly around the body of 

 certain protozoon organisms, and are therefore known as actinopodia 

 (star feet). 



2. Flagella. In protozoa these are tapering filaments, broadest 

 at their attached base and ending in a fine tip. Protozoa may have 

 a flagellum at the anterior or at the posterior end; they may have a 

 flagellum at each end and a large number of them distributed entirely 

 around the body. Dobell distinguished four types, depending upon 

 the origin of the flagellum : One in which the flagellum arises directly 

 from the nucleus; a second, in which the flagellar base is united to 

 the nucleus by a connecting filament, the zygoblast; a third, in which 

 the flagellum arises from a basal granule, which is independent of 

 the nucleus, as in herpetomonas ; and a fourth, in which the flagellum 

 arises from a special kinetonucleus (blepharoblasf), as in trypanosoma. 



3. Cilia. The cilia of protozoa are similar in type to the cilia lining 

 the epithelial cells of the nasal or uterine mucosa in higher animals. 

 They are generally shorter than flagella, and like them broader at the 

 base and pointed at the distal end. They are peculiar in their motion; 

 first they move rapidly and energetically in one direction, and then 

 they withdraw slowly to the opposite direction. This double motion 

 is repeated more or less continually. Cilia generally show a granule 

 at their basal attached end. They may be distributed uniformly 

 over the whole external surface, limited to one-half or to the ventral 

 surface of the body of the protozoon, or arranged in a single circle 

 around the mouth opening. In some cases cilia are united together 

 to a brush, in other cases they are completely fused to membrane or 

 leaf-like masses, which are then called membranelles. The basal 

 granules from which cilia arise have a nuclear derivation, and are 

 called microsomes . In many infusoria such kinetic granules are 

 arranged in threads and rows. They form a contractile substance, 

 evidently related to the muscle substance of higher animals, and these 

 primitive muscles are called myonemes. 



Reproduction. It has been seen that bacteria which have no differ- 

 entiated nuclei multiply simply by binary division or fission. The 

 blastomycetes, yeast cells, or budding fungi, which are somewhat 

 higher in phylogenetic development among the simplest forms of 

 vegetable life, possess a nucleus, and when they multiply by spore 

 formation or budding a division of the nucleus always occurs, with 

 a division of the cytoplasm. All animal cells possess nuclei, and 

 nuclear division always occurs in cell reproduction or multiplication. 

 When the nucleus simply divides as a whole without the formation 





