194 GLOSSARY 



Mol lus'ca, the branch of animals to which clams, snails, etc., belong. 



Mo noe'cious, reproductive organs in different regions of the same individual. 



Mouth, the anterior opening into the digestive cavity. 



Neph rid'i um (pi. neph rid'i a), >■ tubule functioning as a kidney in some 



of the worms. 

 Net'tle cells, the stinging cells found in the coelenterates. 

 Noc tur'nal, pertaining to night. 

 Nu cle'o lu3 (pi. nucleoli), a very small, dense, dark-staining body, either 



within the nucleus or near it. In the latter case it is often called the 



paranucleus or micromuleus. 

 Nu'cleus (pi. nuclei), a dense bit of protoplasm usually near the center of a 



cell, often staining dark. 



cel'lus, a simple eye. 



Om niv'o rous, eating or living upon food of all kinds. 



per'cu lum, a lid or cover. 



O'ral, pertaining to the mouth. 



Oral groove, a funnel-shaped groove in one side of some one-celled animals 



conducting food to the mouth. 

 Or'der, a term in classification used to designate a group of genera. 

 Or thop'ter a, the order to which locusts, grasshoppers, etc., belong. 

 Os'culum (pi. oscula), the large opening from the central cavity in sponges. 

 Os mo'sis, the process by which fluids of different densities become equally 



diffused when separated by an organic membrane or by a porous 



structure. 

 Os'ti a (sing, ostium), the inner ends of the canals in the body-walls of 



sponges. 

 O'va ry, the organ in which the egg cells are developed. 

 vi pos'i tors, organs used to deposit eggs. 



Pal'li al, a line connecting the two muscle scars in a bivalve shell. 



Palp, (i) a jointed finger-like structure on the oral appendages of arthro- 

 pods; (2) oral appendages found in moUusca. 



Pan'cre as, one of the glands of the digestive system. 



Par a nu'cle us, see Nucleolus. 



Par'a si tism, an association of two animals, one living at the expense of the 

 other. 



Pec'to ral, (i) pertaining to the thorax or breast; (2) the anterior of the 

 paired fins of fishes. 



Pelvic, (l) pertaining to the pelvis; (2) the posterior paired fins of fishes. 



Pen, a remnant of exoskeleton found in the squid. 



