174 GENERAL BIOLOGY 



prophase. The preparatory stage of mitosis; the period of 



formation of chromosomes and spindle, 

 prosopyle. In the sponge a pore connecting the incurrent 



and radial canals, 

 prostomium. The region which overhangs the mouth in 



annelids. 



prothorax. The first somite of the thorax in insects, 

 protoplasm. The living substance, 

 protopodite The basal portion of a crustacean appendage 



from which extend the two distal branches, exopodite 



and endopodite. 



protractor. A muscle that draws forward, 

 pseudopodium. A temporary and changing protoplasmic 



projection in amoeba and similar protozoa, 

 pyrenoid. Bright globules embedded in the chloroplasts 



of green algae, which function to produce starch. 



radial. Diverging from a common center, as the radial 



canals of a medusa. 



retractor. A muscle which draws parts back, 

 rhizome. The underground stem of the fern. 



S 



sclerenchyma. Woody or hard cells in plants which serve 

 to stiffen and support. 



secretion. A substance, made by parts or organs of an 

 animal, which is of use within the body. 



septum. A wall or partition, especially the partitions divid- 

 ing the ccelom of annelids. 



serosa. Serous membrane; a delicate tissue which lines 

 closed cavities and is bathed by lymph. 



