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BIOLOGY: GENERAL AND MEDICAL 



spiral is finally surrounded by an unbroken envelope. 

 These branches divide slowly into septa perpendicular 

 to the surface and the envelope consists of short angular 

 cells in which new septa appear parallel to the surface, 

 so that the envelope thickens and is composed of many 

 layers. The small sphere now formed is about . 25 mm. 

 in diameter; the outermost layer is yellow, whilst the 



FIG. 73. Ulothrix zonata. A, Young filament with rhizoid cell, r (X about 

 300); B, portion of filament with escaping swarm spores; C, single swarm spore; 

 D, formation and escape of gametes; E, gametes; F, G, conjugation of two 

 gametes; H, zygote; J, zygote< after peried of rest; K, zygote after division 

 into swarm spores. (After Dodel-Port. B-K X about 482.) 



inner layers remain soft, and later are dissolved. The 

 spiral, after a time, extends and throws out on all sides 

 branched filaments which dislodge the inner layers 

 of the envelope. These branches finally take the form 

 of an ascus, eight spores being formed in each. After 



