Dr. G. C. Wallich on the Diatomacea. 5 



the sand ; and, secondly, the fishes being devoured by the birds, 

 they are voided with the excrementitiotis matter of the latter. 

 As the guano localities are always above the level of the sea, 

 and the species of animalcules yet discovered are all of the cha- 

 racter that inhabit the bottom of the ocean, the most probable 

 reason for their occurrence is that above described/'' 



Now, with one or two rare exceptions, it would be easy to 

 show that no Diatomaceous frustules exist of sufficiently large 

 size to come within the focus of any bird's eye whatever. Nor 

 could any vertebrate animal we are acquainted with, by any pos- 

 sibility, gather together, within a reasonable period, a sufficient 

 supply of such infinitesimal nourishment as the Diatomaceas 

 afford, even granting that the optical difficulty were in any 

 manner overcome. Again, no animal is known to possess pre- 

 hensile or masticatory apparatus of sufficiently delicate arrange- 

 ment to enable it to deal with particles so minute. The presence 

 of Diatoms in guano, therefore, cannot be said to result from 

 their constituting a direct source of food to the birds in question, 

 but from their being the main source of food to the countless mi- 

 nute animals and animalcules, from the Crustacean and Mollusk 

 down to the humblest hydrozoic being, on which the feathered 

 tribes of the open sea depend for diet. 



Touching the position assigned by Professor Quekett to the 

 living representatives of all species whose remains have been 

 found in the guanos, and assuming that the Diatomaeea? were 

 included under the term " animalcules" (which was almost uni- 

 versally applied to these organisms at the time the paper referred 

 to was written), it is only necessary to mention that in no in- 

 stance have living Diatoms been brought up, by the sounding 

 apparatus, from extreme depths. Frustules have been frequently 

 obtained, containing the remains of the endochrome. But this 

 proves nothing beyond the fact that the water, at those great 

 depths, is so highly charged with saline particles as to render it 

 capable of preserving, for an indefinite period, such portions of 

 animal or vegetable matter as may sink to the bottom. It is 

 highly probable, moreover, that, putting aside the Foraminifera, 

 Polycystina, and Diatomacea?, whose softer portions are included 

 within a rigid mineral shell, nothing but the bleached skeletons 

 of all the higher organisms ever reaches the bed of the ocean, 

 every soft atom being resolved into its elements, either mechani- 

 cally or chemically, long before it sinks to its final resting, 

 place. 



In the lowest forms of animal life, the absence of one set 

 of functions is counterbalanced by the introduction of another. 

 We thus find that a simple ciliary apparatus, working continu- 

 ally in the midst of an inexhaustible profusion of alimentary 



