MASTIGOBRYUM. 



[ 416 ] 



MEASUREMENT. 



merged, leafless branches, globular, with a 

 double wall and a central sporophore, some 

 containing racemosely-stalked sacs filled 

 with barren spores, others many simple 

 stalked sacs containing a solitary fertile 

 spore. 



IV. Azolla. Leaves alternate, imbricated. 

 Sporocarps submerged, unlike externally : 

 1. Stalked membranous sacs, irregularly 

 dehiscent, containing stalked sacs filled with 

 barren spores; 2. sessile, solitary or twin 

 cellular bodies, each consisting of a highly 

 developed fertile spore, approximating to the 

 condition of an ovule. 



BIBL. Bischoff, Krypt. Gewdchse, Nurem- 

 berg, 1828, p. 63; Esprit Fabre, Ann. des 

 Sc. nat. ser. 2. vii. p. 221. pi. 12 & 13; 

 Nageli, Zeitschr. fur Wiss. Hot. Heft 1. p. 

 168, Ann. des Sc. nat. 3 ser. ix. p. 99. pi. 8 ; 

 Mettenius, Beitr. z. Kenntn. d. Rhizocar- 

 pen, Frankfort, 1846, Ueb. Azolla, Linncea, 

 xx. (1847), Ann. des Sc.nat. 3 ser. ix. p. Ill; 

 Schleiden, Grundz. d. Wiss. Bot. 3 ed. p. 104 

 (transl. Principles, p. 203) ; Meyen, Beitr. 

 z. Kenntn. der Azollen, Nova Acta, xviii. p. 

 507 ; Hofmeister, Vergleich. Unters. p. 103. 

 pi. 21 & 22; W. Griffith, on Azolla, Cal- 

 cutta Journal of Nat. History, July, 1844; R. 

 Brown, on Azolla, Flinders' Voyage, Botany, 

 612. pi. x.; Henfrey, Trans. Brit. Ass. 1851, 

 Ann. Nat. Hist. 2 ser. ix. p. 447. 



MASTIGOBRYUM. See HERPETIUM. 



MASTIGOCERCA, Ehr. A genus of 

 Rotatoria, of the family Euchlanidota. 



Char. Eye single and cervical; tail-like 

 foot styliform; carapace prismatic, with a 

 dorsal crest. 



M. carinata (PL 34. fig. 46, side view). 

 Foot as long as the body ; aquatic ; entire 

 length 1-72". 



BIBL. Ehrenberg, Infus. p. 460. 



MASTOGONIA, Ehr. A genus of Dia- 

 tomaceae. 



Char. Frustules single ; valves dissimilar, 

 angular, mammiform, orbicular at the base, 

 free from umbilical processes, not cellular, 

 angles radiating. Fossil. 



The (eight) species are interesting from 

 the structure of the two valves of the frus- 

 tules differing. Thus in one, M. crux, the 

 angles and rays are four in one valve, but 

 seven in the other ; in M. actinoptychus the 

 angles and rays are nine in one valve, and 

 thirteen in the other, and so on. Diameter 

 from 1-1600 to 1-360". 



BIBL. Ehrenberg, Ber. d. Berl. Akad. 

 1844 ; Kiitzing, Sp. Alg. p. 25. 



MATONIA, R. Brown. A genus of 



Cyathseous Ferns, with a curious stalked 

 and imbricat^ basin-like indusium (figs. 457, 

 458). Exotic. 



Fig. 456. 



Matonia pectinata. 



Fig. 456. Part of a fertile pinna. Magn. 3 diams. 

 Fig. 457. Indusium opened at the side, showing thecse 



in situ. Magn. 25 diams. 

 Fig. 458. The same with the thecse removed. Magn. 



25 diams. 



MAURANDYA. A genus of Scrophula- 

 riaceae (Dicotyledonous Flowering Plants), 

 the testa of the seed of which is composed 

 of cells with spiral fibrous deposits, forming 

 an elegant microscopic object. 



MEASUREMENT and MEASURES. 

 In this article we shall consider the method 

 of measuring the magnifying power of a 

 microscope, of ascertaining the dimensions 

 of objects, and shall give a sketch of the 

 standard measures in which the dimensions 

 of objects are expressed. 



Measurement of the magnifying power of 

 a microscope. The apparent size which an 

 object will appear to possess under a micro- 

 scope will vary of course according to the 

 power of the object-glass and of the eye- 

 piece used, and the length of the body of 

 the microscope ; and it is a good plan to 

 determine the measurements once for all 

 in the case of the various object-glasses and 

 eye-pieces, keeping them written upon a 

 card, so that they may be readily accessible. 



The apparatus requisite consists of a mi- 

 crometer-slide graduated into thousandths 

 of an inch, each tenth division being marked 

 by a longer line; or two separate slides, 

 one graduated into thousandths, the other 

 into hundredths of an inch ; and an ivory 



