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 mother cell 
Fig. 10b. 
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- “ pseudonavicellae ” because they 
resemble in shape the Diatom Naviculla. 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 
Ripe cyst of Monocystis agilis, x 750, showing the spores 
(pseudonavicellae) within the cyst. After Lankester. 
