KErORT ON THE DIATOMACE.E. 3 



50 metres (27 fathoms), the depths being in all cases carefully recorded, and if this sea- 

 water could be placed in glass vessels covered with suitable glass plates and exposed to 

 diffuse light, so as to avoid the great heat of the direct rays of the sun, after a month 

 Diatoms might appear in some of the vessels. In this manner it is not unlikely that the 

 bathymetrical limit of plant life might be fixed with approximate certainty. Moreover, 

 the great facility with which this method of determination may be practised recommends 

 it as one likely to aid in solving this important problem. 



THE BIOLOGY OF DIATOMS. 



This interesting group of organisms, the knowledge of which we owe entirely to the 

 perfection of the modern microscope, has for upwards of half a century occupied the 

 serious attention of naturalists. 



To the entire series of forms the designation Diatomophycese was given by Eabenhorst 

 and Bacillariece by Kutzing, but the name of Diatomacese is now generally adopted. 



Diatoms may be defined as unicellular alga? having a siliceous coat. Each organism 

 forms a small box, the siliceous walls of which completely enclose a space ; these walls in 

 many, if not in all species, are formed by two distinct plates or valves, each possessing its 

 own hoop, one of which embraces and slides over the other like the tube of a telescope 

 or the lid of a box. This hoop, connecting zone or belt, may be single, double, or of 

 complex structure, as in Rhabdonema, Striatella, and some other species, where it is 

 formed of several hoops. Such a complete individual Diatom is called a Frustule, and it 

 may be viewed from two aspects, to which, however, confusing terms have been applied. 

 Thus Kutzing and W. Smith, followed by the English micrographers, speak of front view 

 when the organism presents its belt to the observer, and side view when its valve is next 

 the eye ; but, as the frustule is formed by two plates joined together, it seems reasonable 

 to speak of the front of the box when the valve is seen, and of the side when the union 

 of the two plates (i.e., the belt) is presented. This latter opinion has been adopted by 

 the German naturalists, who call Kutzing' s side view the secondary view and his front 

 view the primary. In order, however, to avoid confusion, the terms valval and zonal 

 might be applied according as the valve or connecting zone is next the observer. 1 



1 The following arrangement will serve to show the relationship hetween these various terms : — 



C Lateral surface (Ehrenberg). 



(a) Front view (Ralfs/W. Smith, &c), i.e., hoop next observer = i ^^ side (Kutzing). 



I Secondary side (Rabenhorst). 



v Zonal view. 



C Dorsum and venter (Ehrenberg). 

 (6) Side view (Ralfs, W. Smith, fee), i.e., surface of valve next observer = \ Se f ondar y side (Kutzing). 



J Primary side (Rabenhorst). 

 v Valval view. 



