OF THE PROTOZOA. RHIZOPODA. 211 



coui'se. Since there is no appreciable distinction of tissues, not even of 

 integument and contents, the existence of vessels to account for these cui^- 

 rents cannot be presumed. 



A cimous exception appears to exist in Gromia Dujardhiii, the filaments 

 of which exhibit no granules, but are perfectly hyaline, and moreover show 

 no circulation. In their transparency, Sohultze remarks, they resemble the 

 processes of Arcella and Diiffiugia, and so also in the matter of breadth, but 

 differ by their greater length, their finely-pointed extremities, and by their 

 frequent ramifications. This species has also in its principal mass pecuKar 

 coipuscles, roimd, oval, or iiTegular in figure, with a sharp outline, and of a 

 bro"svn coloiu-, differing fi^om all other known elementary particles in chemical 

 reaction, in resistance to alkaline solutions, and to mineral acids, even to 

 sulphuiic. 



Amid the many shifting corpuscles and small globules is a large vesicle, 

 constant in position, alternately collapsing and dilating, and hence called the 

 contractile vesicle (XXII. 4, 5, 6). This organ, which is homologous with 

 the pulsating sacs of Ciliated Protozoa, has not been remarked by every 

 observer, nor in many of the Rhizopoda ; nevertheless we presume it to be 

 an essential organ, and its existence general in the class. Li Arcella a con- 

 tractile vesicle has been seen by many ; in Actinoj)hrys Sol, Claparede has 

 satisfactorily proved it a true sac, ha\ing a resistant membranous wall, and 

 has counted as many as ten such vesicles in Arcella vulgaris ; Auerbach treats 

 of the vesicle as general among Amoehcea ; on the other hand, Schultze 

 was imable to discover such an organ among the many Foraminifera he 

 examined. 



I^iJCLEUs. — Another definite body is mostly chscoverable in Ehizopods, viz. 

 a nucleus in the form of a more or less rounded or oval body, more opaque 

 than the rest of the contents, and consequently more solid in appearance 

 (XXII. 4, 5, 9, 16, 20). In Amoeba and Arcella, Ehrenberg and Siebold 

 admitted the existence of a nucleus ; Schneider says that Amoeha cliffluens 

 and A. racliosa possess one, that a round reddish nucleus having a white 

 nucleolus is present in Difflugia at its hinder end (XXI. 19 a, b,f), and 

 that probably aU the Rhizopoda have such an organ. Kolliker, to whose 

 hypothesis of the ceU-natiu-e of Rhizopods the recognition of a nucleus was 

 of much importance, remarks, " with respect to the nucleus, it really appears 

 to be present in some of them (see Ehrenberg' s figures) ; and where it is want- 

 ing, as in Actinophrys, a true nucleus may have existed at an early period, 

 and be absent only in the full-grown animal, or, again, it may be entirely 

 wanting, and still the animal be regarded as a cell." 



Claparede, on the contrary, denies a nucleus to the naked Rhizopoda, at 

 least to Amceha dijfluens ; and hkewise to the testaceous species, such as 

 Arcella. However, he admits that the usual opacity of the shell is an 

 obstacle to an accurate determination of the question, and remarks, concern- 

 ing the foregoing supposition of Kolliker, that there is no evidence of its 

 truth, and no foundation in fact. 



Schultze has encountered an undoubted nucleus in nine different species of 

 Amoeba, in Diffliigia proteiformis, D. acuminata, and D. Helicc, in Arcella 

 vulgaris and several species of Euglypha. In Ch^omia oviformis a round, 

 clear, delicate body fiUed with very transparent small vesicles may always 

 be found. In old full-grown individuals not one but several such bodies are 

 seen at the posterior part of the animal, all of equal size and of similar struc- 

 ture (XXI. 12, 13, 14). In one specimen as many as eighteen of these 

 nuclei were counted. In young small Gromicf only one nucleus is seen; 

 in a solitary instance two were found. 



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