12 



careful personal manipulation only that results can be obtained 

 which may be relied on, I further procured the necessary ma- 

 chinery and made a large number of sections, in every possible 

 direction, of numerous entire flints*. The results have far sur- 

 passed my most sanguine expectations. I have not only dis- 

 covered, beyond possibility of question, the intimate structure of 

 the Ventriculidas, and in so doing have discovered an entirely 

 new and most remarkable form of animal tissue, but I shall be 

 able to show the cause and character of all the modifications of 

 form under which the Ventriculidse are found ; and I further hope 

 to afford indications (I wish to express myself here as cautiously 

 as possible) of the natural affinities and habits of the living bodies 

 to which these very interesting fossils owe their origin. 



It should be remarked, that the difficulties in the way of obser- 

 vation of structure in chalk specimens is no less, in reality, than 

 of those in flint. The very friable nature of the chalk, coupled 

 with the almost invariable presence of oxide of iron, would be 

 sufficient to obscure and practically to obliterate a structure far 

 less delicate than that of these bodies. Hence the coarser su- 

 perficial characters which have been seized upon by all authors 

 as characteristic of genus are all that is usually visible. It was 

 not without much difficulty and care that I succeeded in exami- 

 ning satisfactorily the intimate structure of these bodies as ac- 

 tually preserved in that matrix. 



It will clearly be only by thus gaining an insight into the true 

 comparative values, if I may so speak, of the facts exhibited by 

 remains preserved in both chalk and flint, that the inquirer can 

 be in a position usefully to commence his researches with the 

 hope of reaching any definite and satisfactory results. 



We find specimens of the Ventriculida? preserved in flint in 

 one of three ways : the place of the body either wholly solid, the 

 crystallized silex having entirely filled up the original hollow : 

 partially solid, and that is generally towards the central parts of 

 the flint, the marginal parts, and especially the roots, remaining 

 the last to be solidly silicified : or, lastly, the Whole occupied by 

 an open network only. Each case may be examined with great 

 instruction, the key to what it teaches having first become 

 thoroughly understood upon the principles above indicated, to the 

 deduction of which principles instances like these were steps, and 

 of which they do but afford illustrations. 



It follows from those principles that, where the calcedonyf, 

 whether solid or open, began by crystallization round some re- 



* The sections of flints usually examined by microscopists are of mere- 

 chips and fragments. They can be of no value in an investigation of this 

 nature. 



f See note Ann. and Mag. for May last, p. 307. 



