OF THE PEOTOZOA. HHTZOPODA. 



237 



pseudopodes, the analogy is not complete, this being a solitary, and the Sponge 

 a compound or aggregate, animal." In a previous pag-e the theoiy of Ehi-en- 

 berg, that the Fomminifera are compound or aggregate animals, has been 

 referred to. It was on this hypothesis that he assumed theii* affinity with 

 Polypes — with Flustrae and Bryozoa, at the head of which he arranged them. 

 This association, like the hypothesis it rests upon, is untenable. In his 

 work on the Foraminifera of the Vienna basin, M. D'Orbigny assigned a 

 position to these animals as an independent class between Echinodeims and 

 Polypes, which, from the present knowledge of the structui^e and reproduc- 

 tion of those classes, we cannot suppose he would seek to maintain. 



CLASSiFiCATioif OF Ehizopoda. — The fii'st division of Rhizopoda that suggests 

 itself is into naked and testaceous forms, or, as Ehrenberg would say, into 

 illoricated and loricated. The naked forms constitute the family Amoehma, 

 represented by the single genus Amoeba. 



The determination of specific characters in this family is attended by almost 

 insurmountable difficulties, and can only be imsatisfactoiy, by reason of the 

 absence of any definite figiu^e, and of determinate organs or parts. More- 

 over the semiiluid body of any one presumed species must be much influenced 

 by external causes, and in some measui-e by the matters which may have 

 entered into its substance ; and the like causes will doubtless operate by 

 modifjing the outline, dimensions, and number of the processes. Among 

 such causes the density of the liquid in which they live, and the quantity of 

 organic matter contained in it, may be particularly mentioned. Claparede 

 remarks — " It appears almost absurd to attempt the distinction of species 

 amongst the Amoehce until we know something more of their intimate 

 organization. Thus Ehrenberg' s A. radiosai^ characterized by the regularity 

 of its processes, and its generally stellate form when at rest ; but when the 

 creature creeps, it slowly expands and the peculiar outline disappears; it 

 flows along like a cloudy veil or di-op of oil, and A. radiosa has become converted 

 into A. diffluens.^^ Yet, this author afterwards goes on to say — "even the 

 changeable Amoebce have their ty[ncal forms, such as the stellate and globu- 

 lar." Other grounds of specific distinction (of no very certain value, indeed) 

 are foimd in the shape, length, and mode of termination of the variable pro- 

 cesses, and in the size, colour, transparency, activity, and habitats of these 

 bemgs. 



The Testaceous Ehizopoda natiu-ally fall into two groups, — one distinguished 

 by having a unilocular, the other a multilocular, shell — the former called, by 

 Sehultze, Monotlialamia, the latter, Polythalamia or Foraminifera. These 

 grand di\isions have been recognized by every natiu^alist ; but some have been 

 led, from giving importance to other particulars, to arrange difierently cer- 

 tain genera, or, otherwise, to detach some as additional families. 



Thus Ehrenberg, swayed by his polygastric hypothesis, and satisfied in his 

 own mind that the ArceUce, Difflugice, and one or two other monolocular genera 

 possessed a series of stomachs and other organs like other Polygastria, imited 

 those genera into a family which he caUed Arcellina. This detachment of one 

 group of pseudopodous beings from the rest, he further justified, as heretofore 

 stated, by representing it to have sihcious instead of calcareous shells. In 

 this dislocation of evidently- aUied forms he finds no imitators, and is unsup- 

 ported by facts. 



D'Orbigny distinguished the one-chambered, sac-like, shelled Ehizopoda 

 as one of the six orders into which he separated the Foraminifera, and named 

 it Monostegia. This order is nearly equivalent to that framed by Ehrenberg, 

 under the title of Monosomatia, to comprehend the genera Gromia, Orhidina, 

 and Ovidina, — a term subsequently borrowed by Siebold, but extended by him 



