XANTHIDIA. 171 



tain bodies named Xanthidia. These present some 

 diversity in shape ; but their general form may be 

 compared to a ball stuck full of pins, each of which 

 has, instead of a head, an extremity split into three or 

 four points, which are hooked downward. Ehrenberg 

 supposed these to be distinct animals, to which he 

 gave specific names ; but they are now known to be 

 the sporangia (or seed-bearing vessels) of certain 

 microscopic plants, the Desmidiacece. How these 

 came to be mingled, in the flints, with products 

 exclusively marine, was the wonder, since it was be- 

 lieved that the Desmids were never found except in 

 fresh waters. 



Dr Wallich finds, however, Xanthidia among the 

 alimentary contents of pelagic Salpce ; with the endo- 

 chrome so fresh as to make it manifest that they had 

 recently been taken into the stomach ; and this far 

 out in the limitless ocean. And even adult Desmidi- 

 acece have been found in the same circumstances ; so 

 that the whole difficulty of the association of these 

 sporangia with marine siliceous organisms vanishes by 

 the discovery that this class of plants is also marine. 



What beautiful chains of mutually dependent links 

 are presented to us in these investigations ! How true 

 is the aphorism that in the works of the all-glorious 

 God nothing 'is great, nothing is small: or, rather, 

 the small is great ; nay, sometimes, as here, the least 

 is the greatest. Take away the invisible Diatom and 

 Foraminifer from the ocean, and what would be the 

 result ? Man would not be cognizant that anything 



