HISTORICAL SUMMARY. ^5 



It would not be right to pass by the labours of MM. Blainville and Defrance in the 

 same field. In the articles which they contributed to the ' Dictionnaire des Sciences Natu- 

 relles ' upon Mollusca and Zoophytes, fossil as well as recent, they gave an account of 

 several new and important types of Foraminifera, without any correct appreciation, however 

 of their real nature. 



The second period in the history of the group of which we are treating commences 

 with the presentation to the Academic des Sciences, in 1825, of M. D'Orbigny's systematic 

 arrangement of the Cephalopoda (lxix), in which he first separated these chambered 

 shells, under the title of Foraminifera, from the Siphonifera ; still retaining the former, 

 however, like the latter, as an order of Cephalopods. The entire group of Foraminifera, 

 as then known to him, consisting of none but multilocular shells, he subdivided into five 

 orders, according to the geometrical plan on which the segments are successively added. 

 In the first of these, Stichosiegues, the segments are arranged end to end in a single 

 line, straight or slightly curved. In the second, Hclicodegues, the segments are in like 

 manner disposed end to end, but their common axis forms a spiral. In the third, Enal- 

 lodeyues, the segments are added alternately on the one and on the other side of the 

 first, along two or even three distinct axes, which may be either straight or curved. In 

 the fourth, Entomostegues, the segments are arranged on the like alternating plan, but the 

 double axis forms a spiral, as in the Helicostegues. In the fifth, Agathistegues, the successive 

 segments cluster one over the other around a central axis, each segment forming half of the 

 circumference. Each of these orders is subdivided into two families, according as the 

 growth of the segments is equilateral or inequilateral. And the characters of the genera* 

 (of which a large number were then first instituted by him) were based in part on the 

 relation of the segments to one another, but chiefly on the number, form, and situation of the 

 apertures of the last chamber. To the foregoing orders he subsequently added that of 

 Monostegues, in which there is but a single chamber, and that of Cgdostegues, in which the 

 segments are very numerous, and are arranged in concentric circles around that from which 

 they originate. 



No suspicion appears at that time to have crossed the mind of M. D'Orbigny, that the 

 place of these organisms might be amongst the lowest, instead of among the highest, of the 

 Invertebrata ; and if his determination of their Molluscous nature was based on any actual 

 observations of these animals in their living state, it is certain that such observations must 

 have been of the most superficial character. As his labours have contributed far more than 

 those of all his predecessors put together, to the extension of our knowledge of the diversified 

 forms belonging to this group, it was most unfortunate that they should have been com- 

 menced and carried on under the influence of views regarding the value of characters which 

 have since been proved to be altogether erroneous. 



A correct appreciation of the differences presented by the members of any natural group 



* A set of models in plaster of Paris, representing on a large scale the generic and sub-generic 

 types of these (so-called) microscopic Cephalopods, was issued by M. D'Orbigny about the same time ; 

 and these have proved very useful in the determination of specimens, whose place in his classification 

 could not readily be ascertained from his descriptions. 



