3G2 Naoliide Yatsu. 



(c) The centriole is usually a smooth sphere, but often has a 

 rough surface. Sometiuies it elongates into a thin rod, while in 

 other cases a process is sent off from it. In Asterias eggs treated 

 with ether, I often meet with Y-shaped centrioles. Besides these 

 abnormal cases, rod and Y-shaped centrioles occur normally in some 

 forms, e. g., in Folystoitmin (Halkin, '0-4, pp. 298-299) ; Pygaera 

 (Meves, '02) ; Blatta (Wassilieff, '04) ; Zoogomis (Goldschmidt, 

 '05, p. 619) ; Didyota (Mottier, '98) ; Stypocaulon (Swingle, '9Y). 

 The centriole usually divides after amitotic fashion. The Schreiners 

 ('05) have observed in Myxine a budding of the rod-like centrioles 

 as has been described by Heidenhain ('96). Mattiesen ('03) seems 

 to have seen that the rod-like centrioles in the egg of a fresh water 

 dendrocoel are divided longitudinally (p. 37). 



{d) The centriole is usually single or double in the aster of 

 dividing cells and double in the resting tissue-cells and germ-cells 

 before their growing period ("diplosome," Zimmermann, '98). 

 When double, they lie close together, excepting those in enlarged 

 centrosomes (PI. Ill, Fig. 52) and in abnormal eggs. Three or 

 four centrioles in an aster have been described in Paludina and 

 Pygaera (Meves, '02) in Haminea (Smallwood, '04, PI. Y, Figs. 

 25 and 28). Lillie draws six centrioles at the central end of the 

 first maturation spindle of Chcetopterus egg ('06, p. 208, Fig. 39). 

 The egg of Cerebratuhis treated with CaClg shows an enormous 

 increase in number of the centrioles (cf. Yatsu, '05, Fig. 10). 



We may define the centriole as follows: the centriole is a well- 

 defined cell-organ comparable to the chromosome in its inherent 

 power to grow and to multiply by binary fission. It never grows 

 beyond a certain limit (exceptionally enlarges and becomes hollow). 

 It is either single or do\d)le, but more than two form abnormal 

 cases (Boveri, '95, p. 60, ct seq.). We are as yet unable to discern 

 what happens when the centriole passes out of sight during the rest- 

 ing stage and in some centrosomes, just as we do not understand 

 the achromatic state of "chromosomes." 



(h) Centrosome. 

 The centrosome is very insignificant in the resting asters of Cere- 



