THE INFUSORIA 



ACINETARIA. The simple fission into two approximately equal 

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

 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 

 the gill of the host to which the animal 

 is attached. The meganucleus becomes 

 elongated and then sends out a broad 



Vertical section through Dfndro- 

 cometes paradoxus, Stein, in an early 

 stage of reproduction. The trans- 

 versely striated curved line represents 



meganucleus (A/) haa begun to con- 

 strict ; the three micronuclei (m) are 

 in the final phase of their mitosis. 



g emmuia* nd Th e f P^udopodial process in the same direction. 



While these nuclear changes are taking 

 place, a curved, transversely-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. This 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- 



/i 



FIG. 32. 



Dendrosoma radiant, Bhrb. Size varies from 

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

 ciliated geromulae in their pouches ; e, smaller 

 bud-liker bodies of doubtful significance. (After 

 Saville Kent.) 



Fio. 88. 



Free-swimming ciliated gem- 

 mula of Dendrosoma. a, mega- 

 nucleus ; b, 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- 



