The Annals and magazine of natural history; zoology, botany, and geology . animal to deal with, we have analmost infinite variety of tests. It follows, therefore, that ifwe attempt to do more than group together the variousmost closely related varietal forms and kinds of test on somedefinite system based on a knowledge of the forces or in-fluences which observation teaches us are the most effec-tive agents in the results produced, we are simply the victimsof an old-world illusion that may serve to amuse, but cannotinstruct, those who indulge in it. The annexed figure (fig. 2) must, for present
The Annals and magazine of natural history; zoology, botany, and geology . animal to deal with, we have analmost infinite variety of tests. It follows, therefore, that ifwe attempt to do more than group together the variousmost closely related varietal forms and kinds of test on somedefinite system based on a knowledge of the forces or in-fluences which observation teaches us are the most effec-tive agents in the results produced, we are simply the victimsof an old-world illusion that may serve to amuse, but cannotinstruct, those who indulge in it. The annexed figure (fig. 2) must, for present purposes,be looked at without referenceto the rectangular plates seen Fig- 2. imbedded at its centre. Asa matter of fact, this par-ticular sketch was made toillustrate a point in connex-ion with Dijffiugia symmetrica^of which mention will be madepresently. Apart, therefore,from the presence of thoseplates and a slight deviationfrom the original outline, whichis by no means uncommon,the figure might represent avarietal form either of-D. mitri-formis or of D. Dr. Wallich on the Rhizopods. 469 If we now take fig. 2 of D. mitriformis as we find it, withits admixture of rectangular plates, we shall recognize in thepresence of the latter and the barely perceptible undulation atthe margin of the mouth of the test, distinct evidence of meta-morphism from the ordinary to the transitional type, of which(as has before been stated) Diffiugia symmetrica is the mostpronounced and aberrant variety. But I would particularlymention that, even as the figure stands, it was not selected toillustrate the earliest and most frequent aspect of raetamor-phism, of which a representation was given in fig. 30 of theseries included in the Annals plate of 1864, showing thewhole of the small quartzose particles or minute diatom-valvesplainly melting, as it were, into the substance of the chitinoidand colloid basis of the stratum on which they rest. The occur-rence of these siliceous plates in t
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondo, bookyear1885
