202 GENERAL HISTOKY OF THE INFUSOKIA. 



arranges in his group of single -chambered or nionolocular shells, yet its 

 meaning may be equally extended. 



It would probably have been correct to have placed the Acmetina (XXIII.) 

 among the Rhizopoda, as another family closely allied to the Amoehina ; but 

 the detail of their peculiarities would have too much embarrassed the general 

 description of structure which we have endeavoiu'ed to give of all the usually 

 acknowledged or true Rhizopoda ; we have therefore preferred to describe 

 them as a subclass in the follo^ving chapter. 



The examination of the Ehizopoda requires to be conducted with great care 

 and skill, — a requirement sufficiently illustrated by reference to the erroneous 

 notions and descriptions of the older observers. They must be viewed in aU 

 positions under different degrees and modes of illumination, by reflected as 

 well as by transmitted light, and, especially in the ease of the testaceous 

 varieties, after submitting them to pressiu^e and to the action of various 

 chemical agents, or, when sufficiently large, after making sections of them in 

 different dii^ections. 



The organic Kving mass of all Ehizopoda is alike, and corresponds with the 

 " Sarcode " of ciliated Protozoa and with the amorphous contractile substance 

 of Hydra and of other low organisms. It appears in the present class a con- 

 tractile, highly elastic, colomiess, almost fluid mucus, hyaline or diaphanous, 

 homogeneous, and in refracting power cliffeiing little from water. Xo di- 

 stiQction into an enclosing fii-mer membrane or integument and contents is 

 discoverable ; and cilia are never found. These characters exist in entirety 

 only in very yoimg animals ; for at a veiy early period molecules, granules, 

 and globules or vesicles, and various foreign particles, make theii^ appear- 

 ance, diminish the transparency, and often impart colour. 



A new species of Amceba, figiu'ed by Schultze, the A. ghhularis, is repre- 

 sented as ha\ing a thin, transparent, colourless lamina of contractile substance, 

 from which the processes are given off, and which surrounds a globular, co- 

 loured, and granular chief or nuclear mass (XXI. 1,2). A similar distribution 

 of the substance of an Amceha into a hyaline colourless cortical, and a granu- 

 lar coloiu'ed medullary portion, is represented by the same author in another 

 species ; and it is moreover a structiu^e homologous vdth that in the allied 

 genus Actinoijlirys (XXIII. 28, 29). As to the assigned character, of the 

 animal sarcode being destitute of a distinct investing membrane or integu- 

 ment, the shell produced by the testaceous forms might be considered equiva- 

 lent to one ; and if some observations hereafter alluded to be correct, a re- 

 sistant integument among the Ehizopoda must be admitted as an estabhshed 

 fact. 



It is possible that in some instances the organic substance has a coloiu' of 

 its own ; for instance, Ehrenberg describes Amoeba pynnceps as having a yellow 

 colom\ However, in general the occiuTence of coloiu- is consequent on that 

 of granules, and on the introduction of food ; and obsen-ation proves that the 

 depth of coloui^ augments ^^ith age, and is otherwise in direct relation with 

 the abimdance of food. The coloui' is usually pretty uniformly diffused. 

 Schultze shows this, and also its relation with the thickly- distributed minute 

 granules, in many Miliolidce, Rotalidce, and Gromice. In larger species (he 

 adds), such as PoJystomella strigilata and Gromia oviformis (XXI. 16), the 

 colour occiu's in scattered and much larger particles or vesicles ; yet under 

 what form soever foimd, it is, in the case of the many-celled or chambered 

 Foraminifera, deepest in the oldest cells, and progressively fades on aj^proach- 

 ing those most recently formed, the last being commonly quite colourless 

 (XXI. 28, 33, 36). Experiment also showed that, by depriving the animals 

 of food wliich could convey colour, other chambers than the last lost their 



