HARDWICKE'S SCIENCE-GOSSIP. 



i93 



GRAPHIC MICROSCOPY. 



By E. T. DRAPER. 



No. XXI.— Group of Foramixifera. 



PPROACHING the 

 lowest forms of ani- 

 mal life, the Fora- 

 minifera, of the class 

 Rhizopoda, isan or- 

 der of considerable 

 importance. The 

 typical animal con- 

 sists merely of a tu- 

 bulous or perforated 

 shell, in some 

 species of most 

 elaborate configura- 

 tion ; or an aggre- 

 gation of silicious 

 particles, enclosing 

 and invested by a 

 living substance. 

 Simple as these 

 animals may ap- 

 pear, they, have 

 claimed the attention of the most distinguished 

 naturalists, from the fact that their imperishable 

 remains constitute the greater part of the solids 

 of the sedimentary strata of the earth, the chalk 

 formations in particular. 



The shells and tests are familiarly known to 

 microscopists, the former especially, and very few 

 cabinets are without these popular slides. Even if 

 space admitted, elaborate description would be 

 unnecessary. The literature of the subject may be 

 found in the writings of D'Orbigny in 1826, Dujardin 

 in 1835, and in numerous memoirs. Most works on 

 the microscope, touching on minute forms of animal 

 life, contain a description, and Dr. Carpenter, the 

 greatest authority, summarizes the subject in the 

 article " Foraminifera," in the present issue of the 

 Encyclopaedia Britannica. 



In reference to the plate representing specimens 



of the shell-type, drawn in relative proportion, and 



found together in the same field of view, it may be 



generally stated that there are two distinctive types of 



No. 249. — September 1885. 



foraminiferous shells, the porcellaneous and vitreous, 

 easily detectable under microscopical power, the 

 one series white and imperforate (Miliolidse), the 

 shell being more or less spiral, made up of a series 

 of half turns ; the other Silicious, or perforate, in 

 which the forms are much more varied. Beyond 

 these groups is a sub-division of the order, the 

 Arenaceous, not so frequently found as cabinet 

 specimens, but as microscopic objects of great 

 interest, where a "shell," in its popular sense, is 

 entirely absent, the creature building up, and holding 

 together by its own bodily substance, a nest, or 

 compacted mass of the minutest particles of sand. 



Dujardin's description in 1835, as to the general 

 character of the animality of the foraminifera could 

 not have been firmly established — forms were 

 numerous, but examination required high micro- 

 scopical power, to establish their classification with 

 the sub-kingdom protozoa, and to reveal the character 

 of that vital translucent substance, capable of extreme 

 attennuation, retraction, self-division and fusion, 

 then termed " sarcode." 



The foraminifera, in their most attractive forms, 

 are microscopic. It would be difficult, without the 

 aid of the instrument, to convey an idea of the 

 elegance of their configuration or their wonderful 

 constructive power, where carbonates and silicates- 

 are moulded into shapes and symmetries curiously 

 diverse, by atoms of glairy plasma, thus secreting 

 a poriferous shell, and pouring itself out in sensi- 

 tive filaments ; this is the ordinary form ; but in 

 the Arenaceous group the slimy life aggregates 

 together the minutest granules of sand, cement- 

 ing and holding them by an investment of the living 

 principle. These Arenaceous "tests," appearing like 

 minute seeds delicately formed of grains, are curi- 

 ously interesting ; globular specimens are seen in 

 rows, on filamentous threads of algae or sponges, 

 sometimes in the form of compacted hard thin rinds, 

 made up of grains of all angles fitted together with 

 curious exactitude, leaving interstices through which 

 pseudopodia emerge : these conditions are rarely to 



