212 GENERAL HISTORY OF THE INFUSORIA. 



In Difflugia ^roteiformis usually several (8 to 12) nuclei are perceptible, as 

 in Gromia oviformis, in the j)osterior portion of the shell. 



The nuclei of freshwater Ehizopocls either appear to be homogeneous deli- 

 cate elastic globules, here and there finely granular, or they resemble the 

 nuclear body of Grojnia oviformis, and consist of a group of small vesicles or 

 globules enclosed by a common membrane (XXI. 14). 



The single nucleus of young beings, Schultze supposes to be derived from 

 the parent animal ; and he fiu-ther presumes that, in the coiu'se of age and 

 growth, this organ is capable of multiplying itself, and may, moreover, serve 

 as a centre aroimd which the fine graniiles of the li^-ing contents aggregate, 

 and that, after the formation of an enclosing membrane, an embrj'o is generated 

 from it. On the other hand, this careful obsei'ver was not able to discover a 

 nucleus in Foramimfera, and admits that the above suppositions are highly 

 doubtful. 



In a large specimen of Gromia Dujardinii, Schultze met with certain en- 

 closed bodies, having a firm shell and granular contents, and only wanting 

 a mouth to complete their resemblance to the parent animal (XXI. 18 a, b). 

 He also cites, as still more questionable examples of a nucleus, a clear spot in 

 the fii'st chamber of Rotalia veneta, and in Textilaria picta, a finely-granular, 

 sohd, and nucleariform body in each of the two last cells (XXI. 32). 



On this point, the presence of a nucleus in Foraminifera, we have the state- 

 ment of Ehrenberg, that in each cell, except the last, there is a coarsely 

 granular yellowish brown mass, which represents an ovary in structiu^e and 

 function. Unfortunately, however, the Berlin microscopist stands alone, both 

 in this observation and in its pendent corollary. Dr. Carpenter uses the 

 word nucleus to signify the primordial mass of sarcode seen in the fii'st 

 cell, of which all the subsequent chambers and their contents may be deemed 

 the ofishoots. 



Scattered among the amorphous granules of the sarcode are, for the most 

 part, numerous refracting coipuscles of less size than vacuoles, which are 

 soluble in ether, and therefore concluded to be fat-globules (XXI. 14-16). 

 There are also other molecules dissolved by caustic potash. It is these 

 various globules and granules that some observers have esteemed to be ova, 

 without, however, any countenance from facts for the supposition. 



To recui' to the naked Ehizopoda, Auerbach, in the essay before quoted, 

 attributes a nucleus to the Amoebcva in general. He remarks that the 

 sohd-looking organ, of a dull aspect and commonly spherical figui'e, noted 

 by certain authors in some Amcebce, is rather the nucleolus than the nucleus, 

 and that the latter is perceptible in the form of a hollow space, oftentimes 

 having a ghstening rosy hue, which surrounds the other like a sac (XXII. 

 4, 5, 9, 10, 11). This sac is sometimes visible as a dark areola, but at others 

 requires the operation of chemical reagents to reveal it, or will manifest itself 

 in dead specimens when all the ordinary vacuoles have disapj)eared. At 

 times, both it and its nucleolus have a dumb-bell figure, and thereby indicate 

 the occurrence of the process of self-division. A similar nuclear sac is men- 

 tioned by Schneider. 



As to its chemical relations, Auerbach found that both nucleus and nucleolus 

 were readily soluble in alkalies, and that they became darker in dilute acetic or 

 sulphuric acid, which also caused the precipitation of a finely-granular matter 

 in the vesicular or saccular nucleus. In concentrated acids they fii^st expanded, 

 and were subsequently dissolved. The generally- assigned character of the 

 nucleus, viz. that it becomes darker on the addition of acetic acid, is true 

 only when dilute acid is used. 



Auerbach discovers a nucleus and nucleolus in Arcella, similar to those 



