NUD 



NUM 



belong to etymology, the latter to syn- 

 tax. 



NOTONECTIDiE (i/oJto?, the back, 

 veto, to swim). A family of the Hydro- 

 corisa, or water-bugs, which swim on 

 their backs, and, from their peculiar 

 aspect, are commonly called boat-flies 

 and water-boatmen. 



NOUN {nomen, a name). A part of 

 speech which denotes an object, or the 

 qualities of an object. When it declares 

 its own meaning, without the addition of 

 another word, it is termed substantive; 

 when it requires to be added {adjici) to a 

 substantive, which stands under (sub 

 Stat) and supports it, and of which it 

 shows the nature or quality, it is termed 

 adjective. 



NOVA'CULITE. Whet slate; a mi- 

 neral substance found in beds in primi- 

 tive and transition clay-slate. 



NU'CLEATED {nucleus, a kernel). 

 Having a nucleus or central particle ; a 

 term applied to the elementary cells of 

 animal tissues, the most important pro- 

 perties of which reside in the nucleus. 



NUCLEOBRANCHI'ATA. The name 

 given by De Blainville to the fifth order 

 of the second section of his second sub- 

 class {Paracephalophor a Monoica). M. 

 Rang makes them the first order of 

 Cuvier's class Gasteropoda, and com- 

 prises under it some of the Heteropoda 

 of Lamarck, and the family Pterotrachees 

 of De Ferussac. 



NU'CLEUS (quasi nuculeus, dim. of 

 nux, a nut). The kernel of a nut. The 

 solid centre around which the particles 

 of a crystal are aggregated. The pulpy 

 conical mass which constitutes the cen- 

 tral part of the ovule in plants. In 

 Astronomy, the term nucleus denotes 

 the apparently solid part or body of a 

 comet, as seen through the hazy atmo- 

 sphere which surrounds it. 



NUCULA'NIUM. A superior, inde- 

 hiscent, fleshy fruit, containing two or 

 more cells, and several seeds, as the 

 grape. By Desvaux it was called bacca, 

 or berry, from which, however, it differs 

 in being a superior fruit. 



NU'CULE {nucula, dim. of nux, a 

 nut). A little nut ; a term applied by 

 Desvaux to the fruit of the oak, the 

 hazel, &c. It is more commonly called 

 glans. 



NUDIBRANCHIA'TA {nudus, naked, 

 branchice, gills). An order of aquatic 

 Gasteropods, which breathe by branchiae 

 unprotected by an external or internal 

 shell. These comprise a part of the 

 236 



naked Gasteropods of Cuvler. They 

 have no shell. 



NULLI'PORA. A family of litho- 

 phytous polyps, the axis of which pre- 

 sents no visible pores on its surface. 

 Some naturalists consider that these 

 mucoso-calcareous bodies are not of ani- 

 mal origin. Of the latter opinion is De 

 Blainville, who is opposed in this matter 

 to Lamarck. 



NUMBER. The abstract idea of num- 

 ber is that of times or repetitions. New- 

 ton defines number as the abstract ratio 

 of one quantity to another quantity of 

 the same species; and hence there are 

 three kinds of numbers — integers, frac- 

 tions, and surds. 



1. Number, Abstract and Concrete. 

 When numbers are used with reference 

 to the things numbered, they are said to 

 be concrete numbers. When used with- 

 out such reference, merely to indicate a 

 certain number of units of the same 

 kind, they are called abstract numbers. 

 Thus 500 is an abstract, 500 pounds a 

 concrete number. An abstract number 

 is a number of times ; a concrete, a num- 

 ber of things. 



2. Number, Perfect and Imperfect. 1 . 

 A perfect number is that which is equal 

 to the sum of all its divisors ; in other 

 words, it is a number whose aliquot 

 parts, added together, make a sum equal 

 to the number itself. Thus, 6 is a per- 

 fect number, for its divisors or aliquot 

 parts are 1, 2, and 3, and the sum of 

 these is 6. So 28 is a perfect number, 

 its divisors being 1, 2, 4, 7, 14, the sum 

 of which is 28. 2. An imperfect number 

 is one, of which the divisors or aliquot 

 parts are not equal to the number itself. 

 Thus, 12 is an imperfect number; for the 

 sum of its divisors, 1, 2, 3, 4, 6, is 16. 



3. Number, Cardinal and Ordinal. 

 Cardinal numbers denote number, as 

 one, two, three, &c. ; ordinal numbers 

 denote the place or number in succession, 

 as first, second, third, &c. This distinc- 

 tion leads to a deceptive mode of speak- 

 ing. " The real distinction is that of 

 numeral nouns and numeral pronouns, 

 to the latter of which the term * ordinal ' 

 might properly be applied. That ' first, 

 second, third,' &c., are properly pro- 

 nouns is obvious, if we consider that, so 

 far as they go, this, that, and the other, 

 would supply their places. The so-called 

 cardinal numbers denote collections ; the 

 ordinal numbers point out only the places 

 of the several units of which a collection 

 is composed. Even one, when its force 



