568 GLOSSARY 



Nematocyst (ne-mat'-o-sist), a stinging cell, as found in the Coelenterata. 



Nephrotome (ne'-fro-tdm), intermediate plate of mesoderm which forms the 

 kidney in embryonic vertebrates. 



Neural (nu'-ral), pertaining to the nervous system. 



Nephridium (ne-frid'-i-um), a small excretory body for collecting and eliminat- 

 ing excretory waste, as found in the earthworm. 



Neurocoel (nu-ro-sel'), the cavity within the spinal cord of chordates. 



Notochord (no'-to-kord), a flexible rod-like body found in all embryonic 

 chordates and in the adult of the more primitive chordates. 



Nucleolus (nu-kle'-o-lus), pi. nucleoli, a small body in the nucleus which disap- 

 pears during mitosis. 



Nucleoplasm (nu'-kle-5-plazm), the clear viscid liquid found in the nucleus. 



Nucleus (nu'-kle-us), pi. nuclei, a central body in most living cells that directs 

 important activities of the cell and which contains the part of the cell 

 responsible for heredity. 



Nymph (nimf), an immature postembryonic stage in the life cycle of insects with 

 gradual metamorphosis. 



Ocellus (o-sel'-us), pi. ocelli, a small simple eye between the compound eyes of 



arthropods. 

 Olfactory (ol-fak'-to-rl), pertaining to the sense of smell. 

 Ontogeny (Sn-toj'-e-ni), the development of an individual. 

 Oocyte (o-o-sit'), a female germ cell during maturation. 

 Oogenesis (o-o-jen'-i-sis), the events leading up to the formation of an egg. 

 Ootid (o-o-tid'), a cell produced by maturation divisions that is to become an 



egg- 

 Operculum (o-per'-ku-lum), the gill cover of the true fish. 

 Optic (Sp'-tik), pertaining to the eye. 

 Oral (o'-ral), pertaining to the mouth. 

 Ornithology (or-nT-thol'-o-ji), a study of birds. 

 Orthogenesis (6r-tho-jen'-e-sis), the theory that animals may overspecialize 



in certain characteristics due to internal factors. 

 Osculum (Ss'-cu-lum), an excurrent opening of sponges. 

 Osmosis (6s-mo'-sis), the diffusion of a liquid through a differentially permeable 



membrane. (See text.) 

 Ostium (6s'-ti-um), an opening, such as the anterior opening of the oviduct. 

 Ovary (o'-va-ri), the female gonad; the gland that produces eggs. 

 Oviduct (o'-vi-dukt), a tube that carries the eggs. 

 Oviparous (o-vip'-a-rus), pertains to animals that lay eggs. 

 Ovipositor (5-vi-pos'-T-ter), egg-depositing structure found in many insects. 

 Ovoviviparous (o-vo-vi-vip'-a-rus), young born alive through hatching of the 



eggs before laying; there is no placenta. 

 Oxidation (ox-i-da'-shun), the chemical combination of oxygen with some other 



substance. 



Paleontology (pal-e-on-tol'-o-ji), a phase of biology dealing with a study of life 



as it existed in the past. 

 Palp (palp), a small projection such as is found on either side of the mouth in 



clams. 

 Pancreas (p&n'-kre-tis), a gland found in the loop of the duodenum; secretes 



pancreatic juice and insulin. 



