of Foraminiferal Structure. 161 



very specific statement: — " The subdivision of tiie Rhizopoda 

 into orders seems to be most satisfactorily accomplisheu by 

 taking as a basis those structural characters which are most 

 expressive of physiological differences. Such characters are 

 presented in tlie form, proportions, and general arrangement 

 of the ])scudopodial extensions ; for, notwithstanding their 

 ap]»arcntlv unrestricted polymorpliismj it will be found that 

 the Khi/.opods present tliree very distinct types of pseudopo- 

 dian conformation^ to one or other of which they may all be 

 referred, and that the groups thus for med are eminently natural. 

 How intimately related these diversities are to those funda- 

 mental potentialities of each type which find so little structural 

 expression in the lowest form of animal life, ajjpears from the 

 circumstance that even a particle of profojjlasyn, detached from 

 the general mass of the hody, icill j^^t forth the pseudopodian 

 extensions characteristic of its type, — those of the substance 

 forced out by crushing the ' test ' of an Arcella having the 

 broad, lobated fjrm of those of the Amoeba, whilst those of 

 the substance forced out in like manner by crushing the shell 

 of a Polystomella have the delicate thread-like character of 

 those of the Foraminifera generally" {op. cif. pp. 14 & 15). 



Here, then, we have a clear and definite admission on Di'. 

 Carpenter's part that the presence of a nucleus and of a con- 

 tractile vesicle is indicative of the highest stage of structural 

 organization of which the Rhizopods arc capable. And I 

 take it for granted, therefore, that, conversely, it is meant to be 

 inferred that the absence of both of these organs indicates the 

 lowest stage, the zero, of organization. Yet, extraordinary as 

 it must appear, it is not upon the presence or the absence of 

 one or other or both of these important specialized organs 

 that Dr. Carpenter has based his classification, but " on the 

 characters presented by the form, proportions, and general 

 arrangement of the pseudopodial extensions " — characters 

 which, even if constant and uniform, could not possibly com- 

 pare with them in point of physiological significance, but 

 which, if shown to be both so inconstant and fluctuating as to 

 present themselves with nearly equal frequency in the highest 

 and in the lowest orders into which the Rhizopods are divi- 

 sible, and even to vary entirely in the same genera, cannot be 

 regarded as otherwise than illusory, and therefore worthless 

 for the pui-pose of ordinal subdivision. 



I do not mean to assert that the evidence of advance from 

 the lower to the higher grade of organization on which I have 

 invariably laid the greatest stress, namely the appearance of 

 a nucleus and a contractile vesicle, may not be accompanied by 

 perceptible differences in the general aspect of the sarcode 



