386 ANIMAL NATURE OF DIATOME^. 



Among Kiitzing's species this could only be referred to 

 C. scotica, to which the author assigns a diameter of ^", 

 whilst Nageli says that his species varies from 0-014'" — 

 0-027'"; but not being able to decide without comparing 

 them together, it is better, to avoid confusion, that the 

 supposed Gallionella should be named Cyclotella Ndcjelii. 

 In this species, which he examined whilst living, Nageli 

 describes and figures a nucleus of colourless mucus 

 attached to the wall of one of the two lateral surfaces ; 

 from this, various colourless mucous threads extend them- 

 selves, (sap currents, as in the Spirogyra^ which run 

 along the wall itself, or more rarely into the cavity, one 

 of which, however, constantly goes across through the 

 axis of the cell, to the central point of the opposite over- 

 lying circular surface, where it forms a nucleus so soon 

 as there appears a diaphragm dividing the cavity itself 

 into two. ihis happens as well in individuals that have 

 no siliceous shield, as in those that possess one ; for 

 Nageli believes the shield to be external, and referable to 

 an extracellular substance. A similar appearance of 

 arachnoid threads radiating from a centre was seen, too, 

 by Klitzing, in Melosira salina. Globules of chlorophyll, 

 says Nageli, are distributed in two circles near the obtuse 

 ends of the cylinder, or are disposed in rays round the 

 nuclei of the two circular surfaces. It cannot be denied 

 that such observations favour the vegetable nature of this 

 being, but certainly they cannot destroy the value of many 

 others that support the opposite opinion. In my Cycl. 

 vielosiroides, named by Klitzing C.Meneghiniana, I observe 

 that the deduplication {sdoppiamento) constantly occurs in 

 individuals of smaller diameter, which on that account at- 

 tain a height proportionally and absolutely greater, that is, 

 a larger breadth of the interstitial ring. The Euganean hills 

 afford a new species to this genus, in their thermal springs. 

 Cyclotella concentrica : C. margine in lateribus secun- 

 darus concentrim definito, radiatim striato. Diameter 

 varying from 0-008'" to 0-02'", and the striated margin 

 occupies about half the radius. 



