Glossary. 437 



Mysis-stage. — A stage in the development of certain Crustaceans 

 (Prawns), in which they closely resemble the adults of a genus (My sis) 

 belonging to a slightly lower group. 



Nascent. — Commencing development. 



Natatory. — Adapted for the purpose of swimming. 



Nauplius-form. — The earliest stage in the development of many Crustacea, 

 especially belonging to the lower groups. In this stage the animal has 

 a short body, with indistinct indications of a division into segments, 

 and three pairs of fringed limbs. This form of the common fresh-water 

 Cyclops was described as a distinct genus under the name of Nauplius. 



Neuration. — The arrangement of the veins or nervures in the wings ot 

 Insects. 



Neuters.— Imperfectly developed females of certain social insects (such as 

 Ants and Bees), which perform all the labours of the community. 

 Hence they are also called workers. 



Nictitating Membrane. — A semi-transparent membrane, which can be 

 drawn across the eye in Birds and Reptiles, either to moderate the 

 effects of a strong light or to sweep particles of dust, &c, from the sur- 



1 face of the eye. 



Ocelli. — The simple eyes or stemmata of Insects, usually situated on the 



crown of the head between the great compound eyes. 

 (Esophagus. — The gullet. 



Oolitic. — A great series of secondary rocks, so called from the texture of 

 some of its members, which appear to be made up of a mass of small 

 egg-like calcareous bodies. 



Operculum. — A calcareous plate employed by many Mollusca to close the 

 aperture of their shell. The opercular valves of Cirripedes are those 

 which close the aperture of the shell. 



Orbit. — The bony cavity for the reception of the eye. 

 Organism. — An organised being, whether plant or animal. 



Orthospermous. — A term applied to those fruits of the Umbelliferae 

 which have the seed straight. 



Osculant. — Forms or groups apparently intermediate between and con- 

 necting other groups are said to be osculant. 



Ova. — Eggs. 



Ovarium or Ovary (in plants). — The lower part of the pistil or female 

 organ of the flower, containing the ovules or incipient seeds ; by growth 

 after the other organs of the flower have fallen, it usually becomes 

 converted into the fruit. 



Ovigerous. — Egg-bearing. 



Ovules (of plants). — The seeds in the earliest condition. 



Pachyderms. — A group of Mammalia, so called from their thick skins, 

 and including the Elephant, Rhinoceros, Hippopotamus, &c. 



Paljeozoic. — The oldest system of fossiliferous rocks. 



Palpi. — Jointed appendages to some of the organs of the mouth in Insects 

 and Crustacea 



