14b 



GUIDE TO THE CORAL GALLERY. 



earliest stage in the interior of a sperm morula (or mother cell which 

 gives rise to the spermatozoa). The parasite grows at the expense of the 

 cell and becomes free of it and actively motile. This is the nutritive or 

 trophic phase, and the organism is termed a trophozoite. The fully- 

 grown trophozoite becomes associated with another like itself, and 

 the two form round themselves a common cyst ; the nuclei of each 

 break up, each nuclear particle surrounding itself with a little of the 

 protoplasm of the mother cell, and becoming a sporoblast or gamete. 

 True conjugation now takes place, each gamete of one motlier cell 



Fig. 10b. 



Ripe cyst of Monocystis agilis, X 750, showing the spores 

 (pseudonavicellse) within the cyst. After Lankester. 



coupling with a gamete of the other, thus forming a " zygote." The 

 zygotes become oval and secrete a tough membrane or sporocyst, 

 thus constituting true spores. Lastly, the protoplasm of the spore 

 divides up into eight sporozoites. Fig. 10b shows a cyst containing 

 oval spores, formerly termed " pseudonavicellas " because they 

 resemble in shape the Diatom NaviciiUa. The spores pass out of the 

 body and are casually eaten by another earthworm ; then the spore 

 cyst ruptures and the sporozoites escape and actively burrow through 



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