100 GENEKAL HISTORY OF THE mFUSORTA. 



from other families having an umbilicus only on one valve — Monostomaticce. 

 In this plan, therefore, Kiitzing assigned to the circumstance of striation an 

 altogether secondary place to that of the existence of a central umbilicus, 

 asserting that the presence or absence of transverse striae was inconstant, 

 and therefore not to be used in generic distinctions. 



Meneghini critically reviews Kiitzing' s system of classification, and points 

 out many anomalies and errors in it. " In the three proposed tribes," re- 

 marks this author, " we have unnatural dismemberments and associations. 

 The same conclusion prevails also in respect to the six orders, as well as to 

 the ulterior divisions in the first two, taken from the continuity or inter- 

 ruption of the striae and the presence of one or two stomatic apertures " {op. 

 cit. p. 492). For instance, he asserts that the character of the median 

 apertiu-e, given as distinctive of Tahellariece from Striatellece, is absolutely 

 false ; and he doubts generally of the presence, constancy, and value of a 

 median aperture in framing such distinctions as Kiitzing has done. The 

 Actiniscece he would separate from the Diatomeae. 



Again, proceeding on the principle that no one character can be allowed 

 an absolute value, he divides the Diatomese into two sections, the Actiniscece 

 and Loricatce. Of the latter he would create 8 families: — 1. Eiinotiece ; 



2. Fmgilariece (imiting with them the Mericliece, Striatellece, and Tahellariece) ; 



3. Melosirece, comprising the Coscinodiscece, Tnpodiscece, Anguliferce, Bid- 

 chdphieoe, smd Angulatce ; 4. Cocconeidece ; 5. Achnanthece; 6. Cymhellece ; 

 7. NaviculecB (with aU the Siirirellece) ; 8. Gomphonemeoi (with aU the 

 Licmopliorece, except the genus Licmopliora)^ 



To the presence or absence of an external muco-gelatinous investment 

 around the silicious frustules, this natui^alist gave little weight in framing a 

 classification, reckoning it, together Tvdth the existence or not of a pedicle 

 or of concatenation, as scarcely admissible in the identification of species. 



On the other hand, Prof. Smith has employed these circumstances, con- 

 sidered in relation to the process of self- division, as the basis of his system 

 of classification. He would look to the phenomena of reproduction as the 

 most sure basis ; but in the absence of precise information, except in a few 

 instances, these are at present inapplicable, and self-division seems to him 

 " to come next in order, as a most important function connected with in- 

 crease and growth, and to supply the necessary variety of phenomena on 

 which to ground our sectional divisions." And he thus proceeds to explain 

 his plan (Synops. i. p. xxviii) : — 



" 1 have therefore separated those forms where self-division is accom- 

 panied by the secretion of a permanent gelatinous or membranaceous envelope, 

 in which the frustules are subsequently imbedded, from those in which such 

 secretion is altogether absent, or is represented merely by a cushion or 

 stipes, to which the frustules are attached by a small portion of their sui'- 

 face ; and I have placed the latter, as of simpler organization, in my first 

 tribe, arranging the genera belonging to it into subtribes, depending upon 

 the permanency or otherwise of the connecting-membrane, another product 

 of the self-dividing process. This enables me to place apart those genera 

 whose species present us with frustules in which the union of the cells is 

 dissolved almost immediately upon the completion of self- division, as well as 

 those where a cushion or stipes still maintains a kind of indirect individuality 

 in the divided frustules, from the genera in which the cells cohere after 

 gemmiparous increase, and by such coherence form filaments of various 

 lengths and forms, allotting the latter to subtribes which respectively pre- 

 sent a compressed filament, a zigzag chain, or a cylindrical thread. In the 



