390 ANIMAL NATURE OF DIATOME^. 



this furrow or canal presents apertures disposed in a 

 regular manner. Kiitzing believes these supposed aper- 

 tures to be sections of the canals themselves, that is, 

 portions of them seen in projection. This opinion is the 

 only one consistent M^ith the fact, that the filament being 

 cylindrical, and therefore presenting itself indifferently on 

 every side, these apparent apertures are always seen 

 arranged near the margin. Ehrenberg's assertion that 

 they are more numerous in some species, does not seem 

 to be confirmed. This appearance is still more compli- 

 cated, inasmuch as these fine tubular canals project from 

 the internal surface of the shield, and a slight furrow 

 externally corresponds with them. This condition is 

 evident in Melosira dlsfans, in which, owing to the 

 greater depth of the furrow, the apparent perforations 

 remain separated from the margin. The interstitial ring 

 presents peculiarities of which we have no instance in the 

 preceding genera. Its tenuity and the great variety of its 

 extension are important characters. But here we must add 

 the very important one of the changes it undergoes during 

 observation. It is not uncommon to see the two halves of 

 the articulation separate themselves slowly, and enlarge at 

 the same time with the ring. This fact is not decisive in 

 respect to the great question of the animal nature of 

 these beings ; for it is not subject to a subsequent con- 

 traction, and because in plants we have the analogy of 

 SpirogyrcR, in which, on the rupture of the outer tube, 

 the extremities of the articulation, which were inflected 

 like the finger of a glove, expand themselves as if by 

 elasticity; but many facts controvert this inference. In 

 support of the opposite opinion, is the frequent enlarge- 

 ment of a particular articulation, in a manner similar to that 

 of the (Edogonia. But Hassall justly observes, " for this 

 endochrome .... never becomes condensed into a dis- 

 tinct organ or sporangium ;" . . . for this reason, the 

 resemblance is reduced to a mere appearance. As to 

 this supposed endochrome, proofs are certainly wanting 

 that it is an ovary, as Ehrenberg supposes ; but they are 



