OF THE PEOTOZOA. CILIATA. 329 



of the nucleus of the impregnated germ-cell, and that of the monad can be 

 diiferent. 



'' Therefore, I infer, that the nucleus of the Polygastric animalcules is the 

 seat of the spermatic force ; it can only be called testis, figuratively, it is the 

 essence of the testis. It is the force which governs the act of propagation by 

 spontaneous fission : and, if Ehrenberg be correct, in viewing the interstitial 

 corpuscles as germ- cells (to which opinion Professor Owen inclines), these 

 essential parts of ova may receive the essential matter of the sperm from the 

 nucleus, which is discharged along with them in the breaking up of the 

 monad, which Ehrenberg regards as equivalent to an act of oviposition ; and 

 impregnated germ- cells may thus be prepared to diffuse through space, and 

 carry the species of Polygastric animalcules to a distance from the scene of 

 Hfe of the parent " (p. 67, Ed. 1849.) 



Lieberkiihn {A. N. H. xviii. 1856, p. 321) makes the nucleolus of import- 

 ance in founding specific characters. He says, that, excepting the eye-point, 

 the nucleolus is properly the only part which distinguishes Oplirijoglena 

 flavkans from Bursaria Jiava. — "This body," he proceeds to say, "is shaped 

 Hke a grain of barley, and is marked at each end with a few sharply-defined 

 streaks or fiuTows ; its length is somewhat more than -^ of a millimetre, 

 its thickness in the middle about y^^ of a millimetre. Its substance has a 

 stronger refractive power than that of the rest of the body, but far less than 

 the fat-hke globules. Under the highest magnifying power, no structure 

 could be distinguished, and it withstands for a considerable time the action 

 of water. The nucleolus is situated on the middle of the nucleus, which is 

 about one-fifth of the entire length of the animalcule, and its breadth in the 

 middle about one-third of its length .... It is of ovate form ; its substance 

 displays no recognizable structure. 



" The nucleolus has very difi'erent characters in all the specimens of Bur- 

 saria flava I have hitherto observed. It was always so small that it was 

 difiicult to find it, and never became visible until the Infusorium was com- 

 pressed, while in Ophryoglena flava it may usually be seen through the 

 integuments. Its form is globular, and it presents no structure. It gene- 

 rally adheres firmly to the surface of the ovate nucleus." 



The same lesson concerning the utility of the nucleus and nucleolus in 

 distinguishing genera and species, might be gathered from the descriptions 

 of Stein and others, which show clearly enough that these organs have a 

 detenninate figure and relation in several genera, as, for example, in Spiro- 

 chona and Paramecium. 



The figure of the nucleus and the relation of the nucleolus to it, in Pro- 

 rodon teres and in Nassula elegans, are deserving attention. In the former 

 species the nucleus is represented as globular, with a nucleolus siu^mounting 

 it (XXVIII. 9) ; in the latter, the nucleus is stoutly clavate, and terminated 

 by a small oblong nucleolus at its narrower extremity. These weU-marked 

 peculiarities in the two examples named, coupled with the views of Lieber- 

 kiihn just cited, and the conclusions of Stein and Balbiani concerning the 

 physiological relations of the two organs in question, wiU challenge for them 

 much more attention than they have hitherto received. 



M. Balbiani has lately contributed to the French Academy two most im- 

 portant papers, in which he has endeavoui^ed to demonstrate a sexual repro- 

 duction of the Ciliata, the nucleus representing the female, and the nucleolus 

 the male, element. In his fii-st essay he illustrates his hypothesis by reference 

 to Paramecium Bursaria {A. N. H. 1858, i. p. 435), and thus writes : — 



" For several generations the Paramecia multiply by spontaneous scission, 

 each of the two new individuals obtaining half the primitive nucleus . . . .' 



