MOLGULA. 



[ 507 ] 



MONADIXA. 



common phenomena. Thus, it prevents 

 turbid water from becoming rapidly clear by 

 repose ; by its agency also the disaggregated 

 particles of animal or vegetable matter are 

 diffused throughout the mass of the liquid. 



The microscopist should become ac- 

 quainted with the appearance of particles in 

 molecular motion, as it might give rise to 

 error; and it often occurs in animal and 

 vegetable cells. Thus particles under its 

 influence might be mistaken for monads ; or 

 particles moved by cilia might be regarded 

 as merely exhibiting this molecular motion. 



Two circumstances appear most favour- 

 able for its production and continuance, in 

 addition to the augmentation of tempera- 

 ture, viz. a very finely divided state of the 

 matter, and the specific gravity of the matter 

 and the liquid in which it is suspended being 

 as nearly as possible coincident. 



BIBL. Brown, On, Active Molecules (pri- 

 vately printed); Duj. Observ. au Mic.; 

 Griffith, Med. Gaz. 1843 ; Delsaulx, M. Mic. 

 Jn. xviii. 1 ; Hartley, ib. 8 ; Jevons, Qu. Jn. 

 Sc. 1878, 167 j Ord, Jn. Mic. Soc. 1879, 

 656. 



MOL'GULA, Forbes. A genus of Tuni- 

 cate Mollusca, of the family ASCIDIAD^E. 



Two British species : M. oculata, adherent, 

 bluish or purple, mottled with orange, 2^" in 

 diameter ; and M. tubulosa, free, in sand. 



BIBL. That of the family. 



MOL'GUS, Duj ., = Bdella pt. 2 species ; 

 on marine sands. (Dujardin, Vlnstitut, 1842, 

 316 ; Gervais, Apt. 158.) 



MOLLUSCA. Every portion of the 

 structures of the Mollusca offers objects of 

 interest to the microscopist. The motion 

 of the cilia, the structure of the lining 

 membrane of the viscera, the spermatozoa, 

 the ovular growth and the nature of the 

 sensory organs can be easily investigated. 

 Remarks upon certain interesting structures 

 occurring in the Mollusca will be found 

 under TONGUE, SHELL, SNAILS (WATER-), 

 MUSSEL, OYSTER, and OVUM. The calca- 

 reous concretions, crystals, and spicula met 



with in the integument or mantle of some 

 mollusca are curious. 



BIBL. Siebold, Vergl. An. and the co- 

 pious BIBL.; Vogt, Zool. Brief e; Adams, 

 Recent Mollusca] Forbes and Hanley, Br. 

 Mollusca ; Woodward, Shells ; Jones, An. 

 Kingdom, and Cycl. of An. and Phys. ; 

 Huxley, Comp. Anat., and EngL Cyclop. ; 

 Deshayes, Hist. Nat. Moll. ; Turton, Br. 

 Shells, by Gray ; Jeffreys, Br. Conch, (figs, 

 of all species, mar. and frw.) ; Rimuier, Br. 

 Id. and freshwater Shells. 



MONACTI'NUS, Bail. A genus of Des- 

 midiaceae = MONACTINIUM, Braun. 



Distinguished from Pediastrum by the 

 marginal cells having one horn only. 

 Species : M. octonarius : marginal cells 

 eight, central none. M. duodenarius (PL 36. 

 fig. 28) : marginal cells twelve, central 

 three. 



BIBL. Bailey, Smith. Contr. 1853, 14; 

 Rabenh. Ala. lii. 71. 



MONADI'NA. A family of Infusoria, 

 according to Ehrenberg's system, but con- 

 sisting of a heterogeneous group of imper- 

 fectly examined bodies. 



Char. Carapace absent ; no expansions ; 

 locomotive organs consisting of one or more 

 flagelliform filaments or cilia at the anterior 

 part of the body. 



Ehrenberg distinguishes nine genera : 



A. Tail none. 



a. K"o lips. 



a. Swimming. 



a. No eye-spot. 



Single 1. Monas. 



Grouped 2. Uvella. 



ft. Eye-spot present. 

 Single. 

 * Flagelliform filaments 



one or two 3. Microglena. 



** Flagelliform filaments 



four or five 4. Chloraster. 



*** Flagelliform filaments 



numerous 5. Phacelomonat. 



Grouped 6. Glenomorum. 



b. Soiling 7. Doxococnts. 



b. Lips present 8. Chilomonas. 



B. Tail present 9. Bodo. 



Dujardin divides them thus : 



MONADLN-A. 



moving throughout its whole length 1. Monas. 



. 



ior prolongation .................. 3. Chilomonaa. 



Two equal filaments terminating the curved angles of the anterior end ........................... 6. Trepomonas. 



Four equal filaments in front, and two thicker ones behind ............................................. 7. Hexamita. 



A second filament arising from the same spot as the flagelliform filament, but thicker, 



trailing and retracting ............................................................................................. 8. Heteromita. 



A filament and vibratile cilia ............. .......................................................................... 9. Trichomonas. 



................................................................................... 10. Uvella. 



ups originally fixed at the end of a branched polypidom or stalk .............................. 11. Anthophysa. 



9 _a f Groups always free, revolving 

 = Exl G ' rou P s originally fixed at the 



