Ookinesis in Cerebratiihis Lactcns. 361 



seem to sn})i)oi't the secretion theory of the nncleohis advocated by 

 Hacker ('99) and recently by Bonnevie ('06)^ bnt is in favor of 

 the transportation theory as has been maintained by Rhumbler 

 ('93, p. 351); Lnbosch ('02); Hcrtwig ('02); Ilartman ('02); 

 Giinther ('03) and others. 



Iir. (UONTUIOLE AND CeNTKOSOMK. 



(a) Centi-iule. 



In a general way the centriole may be said to be a cell-organ, 

 which undergoes very little change during the complicated processes 

 of karyokinesis. The centrioles show, however, in normal as well 

 as in abnormal cases some variation in size, shape, number and 

 position in the centrosome. 



{a) The centriole usually lies at the spot to which the astral 

 rays converge, but sometimes it is found eccentrically in the aster. 

 The segmentation centriole seems to drift about in the degenerating 

 aster, since it is situated at no definite place (PL III, Figs. 43 and 

 45). In an enlarged centrosome the position of the centriole is 

 very variable (PL III, Figs. 50 and 51). 



(h) The size of the centriole seems to be fairly constant in all 

 the cells of a given species, although a slight change in its size can 

 be noticed (Boveri's view of proportionality between the size of 

 cell and that of centriole may not be universally applicable, 'Ofi, 

 p. 96). In fact at its first appearance, it is a little smaller than 

 in a full-grown aster. A considerable diminution takes place in the 

 young cleavage-centriole found near the conjugating germ-nuclei 

 (PL III, Fig. 45). In abnormally treated eggs, e. g., in the 

 CaClo eggs, the centrioles vary in size in an extraordinary degree, 

 ranging from the smallest one but a little larger than the vanishing 

 ])oint up to those almost three times as large as the normal size 

 (Yatsu, '05, Fig. 10). Only a few cases have hitherto been recorded, 

 in which the centriole actually enlarges and becomes hollow. Hacker 

 observed in 8ida the growth of the centriole ('93) ; Conklin in 

 Crepiditla ('01, '02), and in Ciona and Cynthia ('05) ; Small wood 

 in TTamwea ('01, '04) ; Bonnevie in Enf.eroxenos ('06). 



