CARPENTER^ ON FOKAMINIFERA. 29^ 



knowledge of the history of the Foraminifera into four periods. 

 First, the period from the time they first attracted attention 

 to the appearance of D^Orbiguy^s classification of them. 

 Secondly, from the appearance of D'Orbigny^s arrangement of 

 them as mollusca to the announcement by Dujardin of their 

 essentially rhizopod structure. Thirdly, the period which termi- 

 nated with Ehrenberg's great discovery of their abundant 

 presence in the chalk. The fourth period commenced with the 

 researches of Professor Williamson, of Manchester, on Lagena 

 and Polystomella, the latter series of which were first published 

 in the ' Transactions of the Microscopical Society of London.' 



In the second chapter, the structure, organization, and 

 physiology of the Avhole group of rhizopods are treated of, 

 and concludes with some remarks on the reproduction of 

 rhizopods. In this department of inquiry there is yet a field 

 for the labours of the young physiologist. 



The third chapter is devoted to the chief types of structure 

 and Mode of growth of the Foraminifera. It is in this chapter 

 that the general reader and microscopic observer will find 

 most to interest him. The subjects taken up in order are 

 the texture of the shell, its mode of increase, the interme- 

 diate skeleton, the canal system, the separation of segments, 

 the plan of growth, the septal aperture, the form of septal 

 plane, and the nature of the surface marks. 



These subjects are, however, all treated in relation to the 

 principles of classification. Dr. Carpenter, as is evident from 

 his preface, is deeply impressed with the fact that there are 

 no definite limits within which the so-called species can be 

 confined, and he loses no opportunity of impressing this on 

 the mind of his reader. 



The following are the propositions which the author con- 

 siders his researches warrant him in laying down : 



"1. The range of variation is so great among Foraminifera, as to in- 

 clude not merely the differential characters which systematists proceed- 

 ing upon the ordinary methods have accounted specific, but also those 

 upon which the greater part of the genera of this group have been 

 founded, and even in some instances those of its orders. 



" 2. The ordinary notion of species, as assemblages of individuals 

 marked out from each other by definite characters that have been geneti- 

 cally transmitted from original prototypes similarly distinguished, is 

 quite inapplicable to this group ; since even if the limits of such as- 

 semblages were extended so as to include what would elsewhere be 

 accounted genera, they would still be found so intimately connected by 

 gradational links, that definite lines of demarcation could not be drawn 

 between them. 



"3. The only natural classification of the vast aggregate of diversified 

 forms which this group contains, will be one which ranges them accord- 

 ing to their direction and their degree of divergence from a small number 



