2 THE AMERICAN MONTHLY [Jan 



The first object to be recorded in this article is a vari- 

 ation of Coscinodiscus asteromphalus (fi^. 1). Instead 

 of the well-known pattern consisting of a ring of larger 

 areolations surrounding the finely perforated membrane 

 which covers a large polygonal cell, we have a circular 

 ring of brackets projecting inwards to strengthen this 

 delicate membrane or cover. The perforations in the 

 centre of this membrane are excessively minute, and 

 those round it are far more minute than those in an or- 

 dinary asteromphalus. These brackets are very similar 

 in appearance to those supporting the delicate auditory 

 membrane in the pygidium of a flea. 



The second point to record is the discovery of a ter- 

 tiary structute in an asteromphalus of the common form 

 (fig. 8), 



This tertiary structure must be looked for in the in- 

 terior of those secondaries which encircle the finely per- 

 forated membrane. It is hardly necessary to say that 

 these tertiaries are excessively minate. In form they 

 are not unlike the secondaries of Asterolampra vulgaris. 



This is a difiicult image, not only on account of its 

 minuteness, but because of its liability to be merely an 

 interference image. There are certain minute micro- 

 scopic images which, although difficult to see, are never- 

 theless undoubtedly true, for by no known method could 

 they have been caused by interference. There are, on the 

 other hand, some comparatively large microscopic images, 

 which are so likely to have been caused by interference 

 that, apart from some special proof, they cannot be re- 

 garded as true. The Systephania diadema (Stephano- 

 pyxis corona), may be cited as an example of this latter 

 class of objects. There, the structure, comparatively 

 coarse, is one that is in all respects very similar to an in- 

 terference image — so much so that for long I regarded it 

 as such ; but further search revealed a> broken piece with 

 some of the supposed ghost structures sticking over the 



