MERISMOPJSDIA. 



[ 500 ] 



MESODINIUM. 



MERISMOP^E'DIA, Meyen.-A genus 

 of Confervoid Algae, consisting of minute 

 cells, arranged in fours and multiples, form- 

 ing a quadrate layer or plate. Several 

 species are described ; but their relation to 

 Gonium is obscure. Sarcina is placed in 

 this genus by Rabenhorst ; but Sarcina 

 forms a cube. See SARCINA and GONIUM. 

 (Rabenhorst, Fl. Alg. ii. 56.) 



MERIZOMY'RIA, Ktz. A genus of 

 Rivulariaceae. 



C/tar. Filaments moniliform, upper cells 

 subulate, basal cells contained in a mucous 

 matrix, and constituting an amorphous 

 thallus. Freshwater. 



BIBL. Rabenh. Fl. Alg. iii. 224. 

 MERMIS, Duj. A genus of Entozoa. 

 M. nigrescens resembles Gordius, but dif- 

 fers from it principally in the vulva of the 

 female being transverse and situated near 

 the anterior end of the body, whilst in Gor- 

 dius this is placed at the posterior end. 

 Eggs black. 



It is found in the newly dug-up damp 

 earth of gardens, and in the intestines of 

 insects. 



BIBL. Duj. Ann. So. Nat. 2 s6r. xviii. 

 129, and ffelminthes, 294 ; Siebold, Ent. Zeit. 

 1842, 146; Meissner, Sieb. and Roll. Zeit- 

 schrift, 1853. 



MEROT'RICHA, Mer.-A genus of Fla- 

 gellate Infusoria. Free, oblong, green ; fla- 

 gellum single, ventral; with anterior tri- 

 ehocysts. 1 sp., freshwater. (Kent,/w/. 249.) 

 MERU'LIUS, Hall. Dry-re t. A genus of 

 Hymenomycetes (Basidiomycetous Fungi), 

 distinguished by the veiny or sinuously 

 plicate folds of the hymenium, these folds 

 not being distinct from the flesh of the 

 pileus, and forming angular or serrated pores. 

 M. lachrymans is the dry-rot fungus. The 

 mycelium is composed of filaments creeping 

 in the substance of the infected wood, dis- 

 organizing and feeding on this as it decays.. 

 The mass is at first white and cottony, form- 

 ing an effused pileus from 1 to 8" broad ; 

 subsequently ferruginous or deep orange. 

 The irregular folds finally discharge a 

 watery liquid, whence the name. 



The most efficacious remedies against dry r 

 rot are creasote and carbolic acid. Cor- 

 rosive sublimate, though at first efficacious, 

 seems to lose its virtue after a time. 



Several species of the genus have been 

 found in England in addition to M. lachry- 

 mans. 



BIBL. Berk. Br. Fl. ii. pt. 2, 129 ; Sow- 

 erby, Fungi, pi. 113. 



MESOCARTUS, Hassall (Spharocarpug, 

 Kiitz.). A genus of Zygnemaceae (Confer- 

 void Algae), with evenly distributed cell- 

 contents, producing in conjugation a cross 

 branch, in which is formed a round spore. 

 It often happens that all the successive 

 members of a long series of cells conj ugate 

 with another similar series, so as to produce 

 a ladder-like body, the " rounds " of which 

 are formed of the transverse processes (tra- 

 beculce, Kiitz.). The onlv kind of repro- 

 duction yet observed is tnat by the spores 

 formed in the transverse branch from the 

 conjoined contents of two cells ; but it is 

 possible that zoospores and encysted con- 

 ditions of these occur, as in SPIROGYRA and 

 MOUGEOTIA. The stellate encysted bodies 

 found in most of the allied plants have been 

 seen in M. scalaris by Thwaites. Thwaites 

 also observed a division of the contents of 

 the spore into four parts, such as occurs in 



M. scalaris, Hass. (fig. 138, p. 204). 

 Sterile filaments 1-1800 to 1-1440" in dia- 

 meter, 6 times as long ; sporanges oval or 

 round. Hass. pi. 42. 



M. depresses, Hass. Sterile filaments 

 1-2880 to 1-2400" in diarn., 6 to 8 times 

 as long ; spores globose or elliptical. Hass. 

 pi. 44. fig. 1. 



M. intricatus, Hassall, is apparently the 

 same as M. scalaris ; all the other forms 

 may be brought under M. depi-cssus. 



BIBL. Hassall, Alg. 166, pis. 41-45; 

 Kutzing, Sp. Alg. 435; Tab. Pliyc. v. 

 (Spheerocarpus), pis. 5-7 ; Thwaites. Ann. 

 N. H. xvii. 262. 



MESOCE'NA, Ehr. A doubtful genus 

 of Diatomaceae, according to Ehrenberg 

 and Kutzing. 



The bodies referred to this title consist of 

 single siliceous rings, oval or angular frame- 

 works, without a centre, and mostly with 

 external and sometimes internal spines ari- 

 sing from them ; many are fossil. 



Whether they are spicula of Echiiioder- 

 mata or not, remains to be decided. Dia- 

 meter from 1-750 to 1-400". 



M. octogona, Ehr., PI. 25. fig. 1. 



BIBL. Ehrenberg, Ber. Berl. Ak. 1840 ; 

 Kutzing, Bacitt. 139, Sp. Alg. 142. 



MESO'CHRA, Boeck. A genus of Co- 

 pepodous Entomostraca, close to Cantho- 

 camptus. 2 species ; brackish water. (Brady, 

 Copep. ii. 62.) 



MESODIN'IUM, Stein. A genus of 

 Peritrichous Infusoria. Free, ovate, snout- 

 like in front, with a ring of setose cilia 



