ANIMAL NATURE OF DIATOMEiE. 513 



the same. Perhaps Terpsinoe may be placed by the side 

 of BiddulpUia in the Family of Melosirese, by the same 

 character.. Their principal difference from Vittse, is in 

 their transverse as well as longitudinal direction. The 

 Vittse belong to the primary valves as wrell as to the 

 surfaces. These peculiarities of structure are certainly 

 very important, because we must reasonably suppose that 

 they bear a direct relation to the internal organisation of 

 these beings. 



But if we consider that in the same genus {Isthmia), 

 we have two species very similar to each other, one of 

 which always presents those incomplete diaphragms, 

 whilst the other is always devoid of them, we are of ne- 

 cessity led to exclude this character from the basis of 

 classification. 



Page 26. — The colourless membrane, which connects 

 all the internal organs of Diatomese together, constitutes 

 the principal portion of their body, as Ehrenberg has 

 well observed in many places. Its transparency impedes 

 our view of its organisation. It seems that the vesicles 

 observed by Ehrenberg in some species, and supposed to 

 belong to the male organs, were directly hollowed out of 

 this substance. Their dilatation and contraction seem 

 rather to indicate a respiratory function. I believe the 

 tube that runs longitudinally from one extremity of the 

 Naviculse to the other, and perhaps represents their 

 organ of digestion, to be hollowed out, in like manner, 

 from this substance, and void of a proper membrane. 



Page 90. — In the Ceratoneis Fasciola, Ehrenberg 

 describes and figures a distinct median aperture in the 

 centre of the lateral surfaces. 



Page 106. — Kiitzing, in the Phycologia Germanica, 

 assigns to the Naviculae of Micromega pallidum, instead 

 of id of a line, U^ = 0-034'". 



33 



