MOLLUSCA. 



[ 429 ] 



MONADINA. 



cules ultimately become adherent to the 

 thin glass covering the slide. 



This motion is in no way connected with 

 evaporation, for it takes place equally when 

 this is completely prevented, just as when it 

 is not. Neither light, electricity, magnetism 

 nor chemical reagents exert any effect upon 

 it. Heat is the only agent which affects it ; 

 this causes the motion to become more 

 rapid. Hence it might be attributed to the 

 various impulses which each particle receives 

 from the radiant heat emitted by those ad- 

 jacent. Or, as it takes place when the tem- 

 perature is uniform, may it not arise from 

 the physical repulsion of the molecules, un- 

 interfered with by gravitation, hence free to 

 move ? The effect of heat would then be 

 explicable, because this increases the natural 

 repulsion of the particles of matter, as in the 

 conversion of water into vapour. 



Molecular motion plays a part in some 

 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 acquaint- 

 ed with the appearance of particles in mole- 

 cular motion, as it might give rise to error. 

 Thus particles under its influence might be 

 mistaken for monads; or particles moved 

 by cilia might be regarded as merely exhi- 

 biting this molecular motion. 



Two circumstances appear most favour- 

 able for its production and continuance, in 

 addition to the augmentation of temperature, 

 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. R. Brown, On Active Molecules,fyc., 

 Add. Observ. on the same, 8vo (privately 

 printed}; Dujardin, Observateur au Micro- 

 scope-, Griffith, Med. Gaz. 1843. 



MOLLUSCA. Remarks upon certain 



interesting structures occurring in the Mol- 

 lusca will be found under TONGUE, SHELL, 

 SNAILS, WATER, MYTILUS, OSTREA and 

 OVUM. The calcareous concretions, cry- 

 stals and spicula met with in the integument 

 or mantle of some mollusca are curious. 



BIBL. Siebold, Veryleich. Anat. and the 

 copious BJBL. ; Vogt, Zoolog. Briefe ; 

 Adams, Genera of recent Mollusca ; Forbes 

 and Hanley, Brit. Mollusca ; Woodward on 

 Shells ; R. Jones, Animal Kingdom, and the 

 articles in the Cycl. of Anat. and Phys. 



MONADINA. A family of Infusoria, 

 according to Ehrenberg's system, but con- 

 sisting of a heterogeneous group of imper- 

 fectly examined bodies (see p. 347). 



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. No lips. 



a. Swimming. 

 a. No eye-spot. 



1. Single 1. Monas. 



2. Grouped 2. Uvella. 



/3. Eye-spot present. 



1. Single. 



* Flagelliform filaments, 



one or two 3. Microglena. 



** Flagelliform filaments, 



four or five 4. Chloraster. 



*** Flagelliform filaments, 



numerous 5. Phacelomonas. 



2. Grouped 6. Glenomorum , 



b. Rolling 7. Doxococcus. 



b. Lips present 8. Chilomonas. 



B. Tail present Q.Bodo. 



Dujardin's characters are (see p. 348) : 

 animalcules without an integument, consist- 

 ing of a glutinous, apparently homogeneous 

 substance, susceptible of becoming aggluti- 

 nated to other bodies and so drawn out and 

 altered in form, with one or more flagelli- 

 form filaments as locomotive organs, and 

 sometimes lateral or tail-like appendages. 



Dujardin divides them thus : 



FA- 



MONADINA. 



roughout its whole length 



1 1 



. 



I arising obliquely from behind an anterior prolongation 



A second filament, {jsSor" :".: "":::::::: I:::;::::::::::::::::: :::::::::::::::: 



Two equal filaments terminating the curved angles of the anterior end 



Four equal filaments in front, and two thicker ones behind 



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



trailing, and retracting 

 .A filament and vibratile cilia 



1. Monas. 



2. Cyclidlum. 



3. Chilomonas. 



4. Amphimonas. 



5. Cercomonas. 



6. Trepomonas. 



7. Hexamita. 



8. Heteromita. 



9. Trichomonas. 



Groups always free, revolving 10. Uvella, 



Groups originally fixed at the ends of a branched polypidom or stalk 11. Anthophysa. 



