PALEONTOLOGY. 383 



Protozoa. The fossil remains of Protozoa are naturally con- 

 fined to those classes or orders which are shell-producing 

 during life. The most widely distributed fossil representatives 

 of the Protozoa are the Foraminifera or Polythalamia (Reti- 

 cularia, Carpenter), which enter largely into the composition 

 of many marine limestones, and whose occurrence has been 

 known for several centuries to natural historians. The earlier 

 memoirs of Breyn (1732), Soldani (1780), Fichtel and Moll 

 (1803), Lamarck (1804-7), Denys de Montfort (i 808-10), 

 wherein a considerable number of these small forms are 

 described and figured, were followed by the more compre- 

 hensive investigations of Alcide d'Orbigny (1824). These 

 for the first time made the attempt to introduce a systematic 

 order and classification into this group of testaceous organisms, 

 which were still almost universally regarded as mollusca, 

 belonging to the group of cephalopods. 



D'Orbigny distinguished two main groups among the Poly- 

 thalamia, one of which (Siphonifera) contains the chambered 

 shells of the true cephalopods, while the other (Foraminifera) 

 embraces the shells characterised by the perforations in the 

 dividing walls of the chambers. The Foraminifera are then 

 sub-divided by D'Orbigny chiefly according to the external 

 features of the shell, and the number and arrangement of the 

 chambers. 



A number of the species enumerated in the Tableau Method- 

 ique have been made known far and wide by enlarged models, 

 which were distributed to various academies in 1825 and 1826. 

 D'Orbigny also contributed a monograph on the fossil Forami- 

 nifera in the Tertiary deposits of the Vienna basin. 



The advance effected by Ehrenberg's microscopic examina- 

 tion of thin slices of Foraminifera has already been mentioned 

 (p. 326). But although so accurate an observer, Ehrenberg 

 formed fallacious views respecting the organisation of the 

 group, and thought the Foraminifera might belong to the 

 Bryozoa. Dujardin in 1835 contested many of Ehrenberg's 

 conclusions, and demonstrated that the Foraminifera belonged 

 to the Rhizopoda. Williamson, Reuss, and especially W. B. 

 Carpenter, objected to the previous schemes of classification 

 which had been formulated merely upon external features of 

 the skeleton and habits of growth. The investigations of 

 Williamson on the fine details of structure, and the famous 

 work by Carpenter on the Microscopic Structure and Classifica- 



