HISTORICAL SUMMARY. ■» 



by M. D'Orbigiiy ; and the influence of his doctrines upon those who interested themselves in 

 the extension of this department of inquiry was for a long time such, as to prevent any other 

 progress than that which consisted in the discovery of new forms from time to time, and in 

 the reference of these to their places in his classification. 



It was in the year 1 839 that Prof Ehrenberg announced to the Berlin Academy the remark- 

 able results which he had obtained from the study of the Chalk formation ; a large proportion 

 of the material of which he affirmed to consist of the shells, either entire or comminuted, of 

 Foraminifera ; whilst among the types sufficiently well preserved to admit of being deter- 

 mined, he showed that as many as ten could be identified with species now existing (xl). 



The commencement of that fourth period in which the discovery of M. Dujardin has 

 received its full recognition, may be regarded as dating from the appearance of two Memoirs 

 published by Prof. W. C. Williamson (of Manchester) in 1847 and 1848. In the former of 

 these, which was a Monograph of the genus Lagena (cvi), the important truth was for the first 

 time formally advanced in regard to this type, that the comparison of a sufficiently large 

 number of individuals would bring to light such a gradational transition from one supposed 

 species to another, as to demonstrate that their diS'erences must be accounted as of 

 individual variation only ; a truth which has since been not only most fully confirmed 

 by the demonstration of its applicability to the reputed species of every genus of Forami- 

 nifera that has been worked out with similar completeness, but has been found capable of 

 extension to many generic and even to some ordinal differences. The latter was a communica- 

 tion to the Microscopical Society, on the structure of the shell and animal of Polystomdla 

 crispa (cvii), in which for the first time were given the results of a minute microscopical inves- 

 tigation of thin transparent sections of the Shells of Foraminifera, and which must conse- 

 quently be regarded as having furnished the starting-point for all future investigations of a 

 like kind. Among the facts revealed by this method of research were several that became of 

 essential value to myself, in the inquiry on whicii I was engaged at the same time in regard 

 to the structure of Nummulites (xii), and served to confirm the inferences I had deduced 

 from the other features of that important type, as to its participation in the characters of the 

 Foraminifera generally. In the course of that inquiry I made the discovery, not only of an 

 elaborate and previously unsuspected structure in the shell itself, but also of a system of canals, 

 by which it is traversed, and which seems to have an important function in its nutriti(>n. The 

 subsequent examination of the minute structure of the shells of numerous recent types by 

 Prof. Williamson (cvni, cix), Mr. Carter (xvin— xxi), and myself (xiii— xvi), has not only 

 added greatly to our knowledge of the distribution and purposes of this canal-system, but has 

 led to a much more correct appreciation than was previously attainable of the value of the 

 several difi'erential characters presented by the respective types ; and a sound basis has thus 

 been furnished for a truly natural classification, which cannot, however, be erected otherwise 

 than provisionally, until the same kind of investigation shall have been carried through a 

 much wider range of types. 



Among the most important of the recent contributions to our knowledge of the organiza- 

 tion and life-history of the Foraminifera, must unquestionably be ranked the treatise published 

 by Prof. Max Schultze in 1854 (xcvii). The author has enjoyed the opportunity of studying 

 several typical forms of the group in their living state, and has most carefully described and 



