CHAPTER III. 



OF THE FORAMINIFERA GENERALLY ; THEIR CHIEF TYPES OP STRUCTURE AND 

 MODES OF GROWTH, AND THE PRINCIPLES TO BE FOLLOWED IN THEIR 

 CLASSIFICATION. 



5L The group of Rhizopods which is known under tlie designation Foraminifera has 

 been shown in the preceding Chapter to be distinguished from the other great divisions of its 

 class, not only by that investment of the sarcode-body with a calcareous shell which constitutes 

 its most easily I'ecognised feature, but by such a peculiarity in the condition of the sarcode- 

 body itself, as seems to justify a marked separation of the animals which exhibit it from those 

 formed upon the type either of the Amwha or the Actinophrijs. That peculiarity (it may be 

 well to repeat) essentially consists in the absence of differentiation in the semi-fluid proto- 

 plasmic substance of which the body is composed ; its homogeneousness being especially 

 manifested in the freedom and minuteness with which its pseudopodial extensions subdivide, 

 and in the readiness and completeness of their coalescence wherever they come into contact 

 with each other, so as by their ramification and mutual inosculation to form a living- 

 network, along the threads of which a circulation of granular particles is continually taking 

 place. Of the Order Reticularia thus constituted so few other forms exist, that 

 it may be almost said to be synonymous with the group of Foraminifera; and it may 

 indeed be questioned whether in a classification based on physiological principles there is any 

 adequate ground for separating from the calcareous-shelled Miliola (^ 35) either Gromia 

 (•[ 33) whose" test" is membranous (probably chitinous), or Licbcrkuhnia (% 32) which has 

 no firm covering at all. So far as we yet know, there is no difference whatever between the 

 animals of these three types ; and to class them separately, still more to arrange Gromia and 

 Layyim (as Schultze has done, xcvii, p. o2) \i\\}a Arcella z.'ixADiJjhigia, on account of the unilo- 

 cular condition of the " test," would seem just as unnatural as it is now admitted to have been 

 to separate Hydra from the compound Hydroida, and Actinia from the compound Helian- 

 THOiDA, and to group together Hydra and Actinia as naked solitary polypes, whilst their 

 composite representatives were classified according as they form horny or calcareous 

 skeletons. Until, therefore, some more adequate ground bf differentiation shall have 

 been established than any at present known, the group of Foraminifera may be 

 considered as really coextensive with the Order Rhizopoda reticularia; and there 



