GENERAL CONSIDERATIONS 13 



(1883), the cell theory was first applied directly to the Protozoa by Barry 

 (1843), who asserted that Monas and its allies among the flagellates 

 were single cells, and that the nucleus found within them was the equiva- 

 lent of the cell nucleus of higher forms. At the same time Barry expressed 

 the view that cells increase only by division, and he compared the proc- 

 esses of multiplication in Volvox and Chlamydotnonas with the cleavage 

 of eggs (cf. Butschli, 1887, p. 1152). 



Barry's view was accepted, in part, by Owen, who thought, however, 

 that the Infusoria could not be included with the flagellates as single 

 cells because of their differentiation. It was von Siebold (1845) who 

 finally asserted the unicellular nature of all Protozoa. 



Balbiani's researches on the life history of Protozoa at first led him 

 into a curious error, a reminiscence, apparently, of Ehrenberg's and the 

 older point of view. O. F. Miiller had observed and had correctly in- 

 terpreted conjugation in different forms, but his successors down to Bal- 

 biani regarded this as incorrect, maintaining that Miiller had seen only 

 stages in simple division. 



Balbiani (1861) returned to Miiller's view, and clearly stated that, 

 in addition to simple division, another and a sexual method of reproduc- 

 tion occurs. His interpretation of the sexual organs of the Protozoa was 

 given in 1858, when he maintained that the larger of the two kinds 

 of nuclei of Infusoria, the macronucleus, is the ovary, and that the smaller 

 one, the micronucleus, is the testis. He saw and pictured the striped ap- 

 pearance of the micronucleus prior to its division and interpreted the 

 stripes as spermatozoa. The eggs were said to be fertilized in the macro- 

 nucleus, and then deposited on the outside where they developed into 

 new ciliates. Stein at first (1859) opposed this assumption, but in the 

 second volume of his work on the Infusoria (1867), misled by his own 

 Acineta theory, in which certain Suctoria were thought to be stages in 

 the life cycle of certain ciliates, he practically adopted it, maintaining 

 however, that the young forms developed first in the nucleus and only 

 later left the mother organism. Biitschli (1873) was apparently the first 

 to point out Balbiani's error, and in his epoch-making work of 1876, 

 after demonstrating the striped appearance of the nucleus in &gg cells 

 (mitotic figure) during division, he concluded that the "stripings" which 

 Balbiani held to be spermatozoa were no other than this striated con- 

 dition of the nucleus during division. Butschli further showed that dur- 



