22 MORPHOGENESIS IN CILIATES 



divides when motile and produces numerous long chains of 

 tomonts. 



The tomont at the last division is shown in Fig. 9a. Be- 

 tween the ciliary rows, some trichocysts are seen, the origin 

 of which w^ill be considered later. Between the rows 1 and 

 9, we recognize the rows x, y, z and an anarchic field of gran- 

 ules. The latter has been generated by the multiplication 

 of granules of the row a, and will be organized in three rows 

 during the early stage of the formation of tomite. The rows 

 h and c will migrate towards the anterior end and eventually 

 degenerate. The granules of a will multiply again and 

 form one of the thigmotactic fields. 



During all this period, the ciliate is motile ; cilia are to be 

 seen everywhere except on the rows a, h, c. 



It thus appears that, whereas the majority of kinetosomes 

 all over the ciliate produce cilia, the kinetosomes of certain 

 regions are devoid of their characteristic production: cilia. 

 The problems raised by this situation will be discussed in 

 the next chapter. 



Later on, the granules of h and c disappear; the granules 

 of a produce persistent cilia. Here again, it is obvious that 

 the fate of the granules depends on the properties of the 

 underlying cytoplasm. This conclusion is reinforced by the 

 consideration of some abnormal cases in which the granules 

 of h and c also produce cilia. 



The mature tomite also shows this beautiful production 

 of trichocysts. It is again perfectly clear that the trichocyst 

 arises from a granule which has been formed by division 

 of a kinetosome. During the growth of the trichocyst, the 

 granule takes the form of a ring, as centrosomes often do, 

 e.g., in spermiogenesis. The ring seems to become a part of 

 the trichocyst itself. The granule having produced a tricho- 

 cyst seems unable to produce new granules, that is to say, 

 to divide. 



But in Polyspira, the production of trichocysts is not lim- 

 ited to the tomite. It starts before the first division. At 



