384 



THE INFUSORIA 



ACINETARIA. The simple fission into two approximately equal 

 halves occurs in a few simple forms only in this class (Sphaeroplirya, 

 etc.); in others (some forms of Acineta, Tokophrya (Fig. 29, 4), etc.) 



the smaller of the two segments is 

 enclosed in a pouch-like cavity of the 

 larger segment. 



In Dendrocometes (Fig. 31) the difference 

 in size between the two segments is even 

 more pronounced. The three micronuclei 

 undergo their phases of mitosis preparatory 

 to division, in a plane at right angles to 



Vertical section through Dendro- the g 111 of tlle host to which the am ' mal 



cometes paradoxus, Stein, in an early is attached. The meganucleus becomes 



stage of reproduction. The trans- i i j j ii, i u j 



verlely striated curved line represents elongated and then sends out a broad 



the first indication of the band of pseudopodial process in the same direction. 



cilia of the future gemmula. The * 



meganucleus (M) has begun to con- While these nuclear changes are taking 



strict ; the three micronuclei (m) are ^lapp mirvprl trnnovprap.lv etristprl Vwinrl 



in the final phase of their mitosis. P lace > a curved, transvei seiy-striated band 



appears in the protoplasm, which is con- 

 tinued after division of the nuclei into a complete circle embracing three 

 micronuclei and one meganucleus. The protoplasm enclosed by this band 

 is then detached from its surroundings and rotates slowly for a time by 

 means of an equatorial girdle of cilia. It then breaks through the body 

 wall of the parent and swims away. TMs remarkable ciliated daughter 

 segment may be called a "gemmula" (Fig. 86). 



In Dendrosoma (Fig. 32) 

 several daughter segments en- 

 closed in incubatory pouches 

 are formed in different parts 

 of the branching body at the 

 same time, and these cannot be 

 regarded as essentially dis- 



FIG. 32. 



Dendrosoma radians, Ehrb. Size varies from 

 1-2 mm. in height, d, base of attachment; c, 

 ciliated gemmulae in their pouches ; e, smaller 

 bud-like bodies of doubtful significance. (After 

 Saville Kent.) 



FIG. 33. 



Free-swimming ciliated gem- 

 mula of Dendrosoma. a, mega- 

 nucleus ; 6, b, b, contractile 

 vacuoles. (After Saville Kent.) 

 x 600. 



tinct in their nature or in their mode of formation from the 

 single internal daughter segment of Dendrocometes. The reproduc- 



