10 HISTORICAL SUMMARY. 



most beautifully delineated the remarkable phenomena which they pi'esent. His observations, 

 which fully confirm and supplement those of M. Dujardin, at present constitute our best 

 source of knowledge on this part of the subject ; and they have since been extended by further 

 researches (xcviii,xcix), especially in regard to the Reproductive processes, which still, however, 

 greatly need elucidation. In his investigations of the structure of the testaceous coverings of 

 these animals, on the other hand. Prof. Schultze has been less successful, in consequence (as it 

 would appear) of his want of acquaintance with the best method of preparing thin sections of 

 them ; and he has consequently fallen into some important errors (such as the denial of the 

 existence of the canal-system, of which the most perfect demonstration is now afforded by the 

 examination of the internal casts of these organisms, to be presently noticed), and has failed to 

 obtain that insight into the real relations of the forms he has studied, which could alone justify 

 him in proposing a new distribution of the group. Although his Classification is in many 

 respects an improvement upon that of M. D'Orbigny, yet (as I think I shall hereafter 

 succeed in showing) it is so far from satisfactory as to leave the way quite open for another 

 attempt, based upon a more thorough knowledge of the objects to be systematically grouped. 

 A Classification still more recently proposed by Prof. Bronn (xi) is chiefly founded 

 upon that of M. D'Orbigny, whilst it adopts certain modifications proposed by Prof Schultze. 

 It cannot, in my opinion, be regarded as less open to objection than either of the systems for 

 which it is proposed as a substitute. 



An entirely new and most valuable source of information in regard to the organization of 

 the Foraminifera has recently been afforded by the discovery, first announced by Prof. 

 Ehrenberg (xLiii) in 1853, that their shells occasionally undergo an infiltration of silicate of 

 iron, that completely fills, not merely their chambers, but their canal-system, even to its 

 minutest ramifications ; so that if a shell thus infiltrated should itself undergo decomposition, 

 a perfect internal cast remains of the original body of the animal, with its extensions through- 

 out the shell. Of such casts it has been shown by Prof. Ehrenberg that the Green Sands 

 which present themselves in various geological formations, from the Silurian system upwards, 

 are in great part composed: and his discovery has thus a twofold value, as, on the one 

 hand, it places before us far more exact representations of the configuration of the animal body, 

 and of the connexions of its different parts, than we could obtain even from living specimens 

 by dissolving away their shells with acid (its several portions being disposed to heap them- 

 selves together in a mass when they lose the support of the calcareous skeleton) ; whilst it 

 also enables us to identify with great certainty the types of Foraminifera by which these casts 

 were originally formed, notwithstanding the entire destruction of their shells. It was soon 

 afterwards shown by Prof. Bailey (U. S.) that a like process of infiltration is taking place at the 

 present time over certain parts of the ocean-bottom (iii), and that beautiful internal casts are 

 obtainable by treating with dilute acid Foraminiferous shells whose cavities have thus filled. 

 By the application of this method to portions of Mr. Jukes's Australian dredgings, Messrs. 

 W. K. Parker and T. Rupert Jones have obtained a series of internal casts of most wonderful 

 beauty and completeness, which I have had the advantage of carefully examining ; and it is 

 with great satisfaction that I can state that in no instance has this examination afforded any 

 other result, than that of confirming the conclusions to which I had been previously led by 

 the study of the shell. 



A very different line of inquiry has been recently prosecuted with great success by the 



