Encyclopaedia Britannica, 11th Edition, "Foraminifera" to "Fox, Edward"

Encyclopaedia Britannica, 11th Edition, "Foraminifera" to "Fox, Edward" - Volume 10, Slice 6

FORAMINIFERA, in zoology, a subdivision of Protozoa, the name selected for this enormous class being that given by A. DOrbigny in 1826 to the shells characteristic of the majority of the species. He regarded them as minute Cephalopods, whose chambers communicated by pores (foramina). Later on their true nature was discovered by F. Dujardin, working on living forms, and he referred them to his Rhizopoda, characterized by pseudopodia given off from the sarcode (protoplasm) as organs of prehension and locomotion. W.B. Carpenter in 1862 differentiated the group nearly in its present limits as Reticularia; and since then it has been rendered more natural by the removal of a number of simple forms (mostly freshwater) with branching but not reticulate pseudopods, to Filosa, a distinct subclass, now united with Lobosa into the restricted class of Rhizopoda. Anatomy.Protista Sarcodina, with simple protoplasmic bodies of granular surface, emitting processes which branch and anastomose freely, either from the whole surface or from one or more elongated processes (stylopods); nucleus one or more (not yet demonstrated in some little known simple forms), usually in genetic relation to granules or strands of matter of similar composition, the chromidia scattered through the protoplasm; body naked, or provided with a permanent investment (shell or test), membranous, gelatinous, arenaceous (of compacted or cemented granules), calcareous, or very rarely (in deep sea forms) siliceous, sometimes freely perforated, but never latticed; opening by one or more permanent apertures (pylomes) or crevices between compacted sand-granules, often very complex; reproduction by fission (only in simplest naked forms), or by brood formation; in the latter case one mode of brood formation (A) eventuates in amoebiform embryos, the other (B) in flagellate zoospores which are exogamous 629 gametes, pairing but not with those of their own brood; the coupled cell (zygote) when mature in the shelled species gives rise to a very small primitive test-chamber or microsphere. The adult microspheric animal gives rise to the amoebiform brood which have a larger primitive test (megalosphere); and megalospheric forms appear to reproduce by the A type a series of similar forms before a B brood of gametes is finally borne, to pair and reproduce the microspheric type, which is consequently rare. ......Buy Now (To Read More)

Product details

Ebook Number: 35925
Author: Various
Release Date: Apr 20, 2011
Format: eBook
Language: English