232 INFUSORIA. 



resembles the excretory apparatus of the flat-worms, that we need 

 hardly scruple to claim for it a similar excretory function, and regard 

 it as expelling the superfluous water and the waste products of 

 metabolism. 



The Nuclei, as well as the contractile vacuoles, lie in the cortical 

 layer. This is especially the case with the nucleus par excellence, 

 which is seen usually, even on superficial observation, and still better 

 after the use of acetic acid, as a conspicuous, firm body, sometimes 

 showing a division into two or more parts of round, elongated, or 

 occasionally ribbon or garland -like form, and whose resemblance 

 to a ordinary cell - nucleus first suggested the idea that the In- 

 fusoria were unicellular organisms. But even von Siebold found 

 besides this nucleus, and generally closely adjacent to it, the so-called 

 " nucleolus " a sharply defined, minute, shining body more than one 

 sometimes being present, although it has not been demonstrated in by 

 any means all the species. 



Both bodies are not only of high importance in determining the 

 morphology of the Infusoria, but have been the subject of much dis- 

 cussion and study during the gradual development of our knowledge 

 of the reproductive process in the Infusoria. For a while the opinion 

 seemed plausible that these two structures represented the sexual 

 organs. This theory was especially based on the observations and 

 conclusions of Balbiani, 1 and was very generally accepted, 2 especially 

 as it seemed in a satisfactory way to sum up a series of more or less 

 unco-ordinated results. 



According to the theory supported by Balbiani, the nucleolus is 

 the male reproductive gland in its undeveloped state, and the nucleus, 

 which Ehrenberg had previously called the " testis," is, indeed, the 

 ovary. 3 Appearances are certainly in favour of such a theory. One 

 sees the nucleolus swell up under certain circumstances, and become 

 a long vesicle, whose contents gradually assume a striated appearance, 

 as if they were a bundle of spermatozoa. 4 While the nucleolus under- 

 goes these changes, and finally divides into a number of balls, re- 

 sembling sperm-capsules, the nucleus, which is meanwhile much 

 enlarged, also falls asunder into a number of round masses, which 



1 " Recherches sur les phe'nomenes sexuels chez les Infusoires," Journal dc physiologic, 

 t. iv., 1862. 



9 The account given of the sexual reproduction of the Infusoria in the first edition of 

 this work owed its origin to the influence of this theory. 



3 According to Ehrenberg, the sperms gained the exterior by means of the "con- 

 tractile bladder," which thus became a sort of seminal vesicle. 



4 Joh. Mxiller, Lieberkuhn, and Claparede and Lachmann had remarked this appear- 

 ance before Balbiani, and had noted the likeness between the threads and spermatozoa, 

 without, however, identifying the two. 



