STUDIES ON CILIATED CELLS 257 



nucleus is situated, so that it takes the form of a pear. Al- 

 though the distal border of the cell in question becomes dimin- 

 ished in extent, I have never been able to find that it becomes 

 rounded off, after separating from the surface of the epithelium, 

 as described by Wallengren. In some cases the distal border 

 is either bulged (fig. 19) or indented, in consequence of the 

 pressure of neighboring cells. The cuticular border, so far as 

 can be seen from our materials, is left intact throughout the proc- 

 ess of cell-division. Since the basal corpuscles are lost to 

 view, the limits between the cytoplasm and the cuticle become 

 indistinct, so that it looks as if the cuticle had disappeared, as 

 Wallengren asserts. 



Metaphase (fig. 19). The plane of division, so far as could be 

 observed, is at right angles to the surface of the epithehum, so 

 that the two resulting daughter-cells lie side by side. 



Anaphase {fig. 20). The chromosomes send off lateral 

 branches which join or anastomose together in a reticular man- 

 ner while the nuclear membrane and nucleolus reappear. The 

 cytoplasmic fission sets in at the inferior end of the cell and grad- 

 ually proceeds upwards. Near and below the cuticle there ap- 

 pear the so-called intermediate corpuscle, from which proto- 

 plasmic filaments run towards the centrosomes. The chondrio- 

 contes, again becoming deeply stained, are arranged in the ver- 

 tical direction, and are chiefly accumulated below the cuticle; 

 the cell becomes in the meanwhile lengthened out downwards. 

 Next, basal corpuscles and cilia make their appearance, which 

 process will be referred to later on. 



Although I have subjected various epithelial tissues of verte- 

 brates to a careful examination, I have never been able to find 

 karyokinetic division of the ciliated cell ; the mitotic figures which 

 are often seen in the ciliated epithelium, do not belong to ciUated 

 cells, but either to non-ciliated columnar, or to basal cells or to 

 glandular cells. 



Summary 



1. The centrosome can be detected in ciliated cells of both 

 invertebrates and vertebrates. 



