PROTOZOA 21 



the Eadiolarian ; more recent research has, however, shown that 

 they continue to live after the death of the animal, that they 

 multiply in more than one way, occasionally forming mobile 

 swarm-spores, that similar cells occur in the tissues of many 

 Coelenterates, and that they contain chlorophyll, although this 

 colouring matter is masked by a yellow pigment. A nucleus 

 and a cellulose cell-way are also present. These features have 

 caused these yellow cells to be regarded as unicellular algae, 

 living in a state of commensalism with the. Eadiolarian, and 

 they have received the name of Zooxanthella nutricola. They 

 are not found in all species, and are usually absent in 

 Acanthometra, and in the other species with a horny skeleton. 



The protoplasm contains, in addition to the yeUow cells, 

 numerous oil or fat globules, and crystals and concretions of 

 unknown use. 



No conjugation has ever been observed in this class ; repro- 

 duction is sometimes by simple fission, which commences first in 

 the central capsules. Spore formation in the central capsules 

 also takes place, and results in the formation of mobile spores ; 

 but the details are complex, and the exact sequence of events 

 not thoroughly understood. 



Many form colonies by the fusion of their extracapsular 

 protoplasm. That of Gollosoum, the individuals forming which 

 are devoid of skeleton, may be an inch or more long. The 

 various members of the colony are held together by a gelatin- 

 ous matrix. 



Group B. COETICATA. 



The animals which are grouped together in this second 

 division of the Protozoa have as a common feature a differen- 

 tiation of the protoplasm into a more fluid central portion and 

 a firmer cortical layer usually associated with a limiting mem- 

 brane, which surrounds their body and gives it a definite shape. 

 As a consequence of the presence of this cortical layer, these forms 

 which take solid food have acquired one or more channels through 

 which the nutriment is ingested, and usually a definite area 

 whence the undigested remnants are extruded. The parasitic 

 forms which live in the nutritive fluids of their hosts, are 

 usually devoid of any such cell mouth or anus. The presence 



