325 Dr. Wallich on the Rhizopods. 



But it would obviously be the height of rashness and an 

 indication of great want of discriminative tact to entertain the 

 idea that whatap}3ears to be a rationally grounded explanation 

 in the case just cited, stands on a par with that involved in 

 the construction of all the varied and complex forms of Fora- 

 miniferal shell. Here we meet with presumptive evidence 

 of the interposition of some faculty superior in kind to that by 

 which the creature is enabled to select from the materials 

 within its reach those materials best adapted for its require- 

 ments. That the Difflugidj,«, in like manner with other 

 Protozoa, do possess and are able to exercise some such faculty, 

 is almost as certain as that two and two make four. Several 

 extraordinary oceanic examples of this were recorded by me 

 as long ago as the year 1858, and frequently since that period. 

 But in the Foraminifer there resides not only a like selective 

 power, when the necessity arises for its exercise^ as we see in 

 the case of the Lituoline and Arenaceous series generally, 

 when seemingly forced to employ sandy or other particles for 

 the consolidation of their shells on account of the supply of 

 carbonate of lime held in solution in sea-water, falling short ; 

 but likewise a constructive faculty of so marvellous a nature 

 as to leave us in a state of utter bewilderment at the beauty and 

 symmetry of construction we see before us. For, be it ob- 

 served, there is in this instance no tangible basis on which we 

 could attribute what we see to the interference of some known 

 extrinsic force, such as chemical affinity or a modified form 

 of crystallization in presence of a colloid. In this dilemma 

 how are we to account for so truly extraordinary a phenome- 

 non exhibiting itself at the very bottom of the animal series ? 



On my own behalf I can only confess my utter inability 

 to suggest a solution of the problem. 



The mquiry having thus, step by step, reached the point at 

 which any special group of characters observable in the testa- 

 ceous Rhizopods under notice can be tested on the basis laid 

 down in the opening paragraph of this paper, let us now turn 

 our attention to Prof. Leidy's monograph on " The Fresh- 

 water Phizopods of North America," the most recent and by 

 far the most beautifully illustrated work on the subject that 

 has hitherto been published ■^. 



The first point deserving of notice is that Prof. Leidy does 

 not ofier any definite classification of his own of the freshwater 

 Phizopods, but confines himself to furnishing a more or less 

 general outline of classification of the various systems pro- 

 posed by Dujardin, Hajckel, Carpenter, Wallich, Huxley, 



* Publislied at Washington in 1879, under the auspices of the " United 

 States Geological and Geographical Survey of the Territories." 



