Dr. Carpenter on the Rhizopod Type of Animal Life. 79 



definiteness there is in the form and structure of the sarcode body 

 that forms the shell ; so that the wonder is, not that there should 

 be a wide range of variation both in the form and in the plan of growth 

 of the aggregate body, and in the mode of communication of the 

 individual segments, but that there should be any regularity or con- 

 stancy whatever. But it is only in the degree of this range that 

 this group differs from others ; and the main principle which must 

 be taken as the basis of its systematic arrangement, — that of ascer- 

 taining the range of specific variation by an extensive comparison 

 of individual forms, — is one which finds its application in every 

 department of natural history, and is now recognized and acted on 

 by all the most eminent zoologists and botanists. There are still 

 too many, however, who are far too ready to establish new species 

 upon variations of the most trivial character, without taking the 

 pains to establish the value of these differences by ascertaining their 

 constancy through an extensive series of individuals, — thus, as was 

 well said by the late Prince of Canino, "describing specimens instead 

 of species," and burdening science not only with a useless nomen- 

 clature, but with a mass of false assertions. It should be borne in 

 mind that every one who thus makes a bad species, is really doing a 

 serious detriment to science ; whilst every one who proves the 

 identity of species previously accounted distinct, is contributing 

 towards its simplification, and is therefore one of its truest bene- 

 factors. 



Some of the most interesting physiological and zoological con- 

 siderations which connect themselves with the study of this group 

 having thus been noticed, its geological importance has in the last 

 place to be alluded to. Traces, more or less abundant, of the ex- 

 istence of Foraminifera are to be found in calcareous rocks of nearly 

 all geological periods ; but it is towards the end of the Secondary, 

 and at the beginning of the Tertiary period, that the development 

 of this group seems to have attained its maximum. Although there 

 can be no reasonable doubt that the formation of Chalk is partly 

 due to the disintegration of corals and larger shells, yet it cannot 

 be questioned that in many localities a very large proportion of 

 its mass has been formed by the slow accumulation of foraminiferous 

 shells, sometimes preserved entire, sometimes fragmentary, and some- 

 times almost entirely disintegrated. The most extraordinary mani- 

 festation of this type of life, however, presents itself in the " num- 

 mulitic limestone," which may be traced from the region of the 

 Pyrenees, through that of the Alps and Apennines, into Asia Minor, 

 and again through Northern Africa and Egypt, into Arabia, Persia, 

 and Northern India, and thence (it is believed) through Thibet and 

 China, to the Pacific, covering very extensive areas, and attaining a 

 thickness in some places of many thousand feet : another extensive 

 tract of this nummulitic limestone is found in the United States. A 

 similar formation, of less extent, but of great importance, occurs in 

 the Paris basin ; and it is not a little remarkable that the fine-grained 

 and easily-worked limestone, which affords such an excellent material 

 for the decorated buildings of the French metropolis, is entirely formed 



