ANIMAL NATURE OF DIATOMEiE. 45? 



Kiitzing describes and figures the Naviculse as disfigured 

 by desiccation, I ought to state that I have observed 

 such Naviculee and thought them specifically character- 

 isticoi a Sc/iizonetna, which, for this reason, 1 denominated 

 S. Cercaria. I have ascertained subsequently that the 

 Naviculie of many species undergo a similar alteration. 

 It takes place more frequently in the Micromegm or true 

 Schizonemce of that genus than in Monnemcs. It ap- 

 pears that sometimes, perhaps in certain physiological 

 or abnormal conditions, the solid substance of the shield 

 is redissolved. The appendages, too, with which the 

 disfigured Naviculse seem, in such cases, to be furnished, 

 are due to the partial tube, which closes upon them 

 {vi si addossa), grows thin, and bursts. 



43. MiCROMEGA. — " Phycoma Jiliforme ramosmn, tubo 

 comnnmi externa cinctum, ex naviculis seriatis compo- 

 situm. Series navicularum singulares tubulis internis 

 minorihus propriis {secundariis) vel fihris tenerrirrds cur- 

 vatis bicrispis cinctce. Spermatia immersa, ex dilatatione 

 navicularum oriunda." 



From what has previously been stated, it would seem 

 to be proved that, by the laws of nomenclature, we ought 

 to maintain the name of Schizonema for this genus : 1st. 

 Because Agardh established this genus (Systema, 1824) 

 with a definition indicating an essential generic character 

 which distinguishes it from the preceding, " fila fascim- 

 forniia e filis angustioribus coadunatis composita, granula 

 elliptica includentibits, in quce iterum secedunt." 2d. Be- 

 cause, in the very description succeeding the definition, 

 he insists upon this organic condition " Composites 

 {plantce) sunt epluribus individuis licet jilif or mibus, iterum 

 includeniibus eadem fere corpuscula qum in Frustulia et 

 Meridione invenimus." And he adds this excellent cha- 

 racter of the mode of branching, " ^arao^a apparent, et 

 ab auctoribus ita describuntur, quod tantum ex fissione 

 Morum oritur." 3d. Of the ten species ascribed in this 

 work, for the first time, and all contemporaneously, to 



