THE MITOTIC CYCLE 



meiotic stages. From them develop the axial filaments of the future 

 sperm tails (Figure 38). 



Since the centrioles of the spermatocyte generally become the 

 blepharoplasts of the sperm tails, the presence of these granules in the 

 spermatogonia may be related only to their future function, and not 

 necessarily to the achromatic figure in the preceding cell divisions. 

 However, in Ascaris megalocephala, the sperm has neither tail nor axial 

 filament, yet centrioles are found in the developing sperm cells, similar 

 to those of the fertilized egg. This fact has been confirmed by Stur- 

 DiVANT.^^^ A converse relationship is found in the cryptogamic plants, 

 which have motile male gametes, the flagellae of which are provided 



a 



sfsS 



---^^ii^^/^;. 



m ^... 



^ — ..■■■■■^■■7%^ 







d 



Figure 39 Progress of the formation of an aster-like figure when i per cent 

 osmic acid is added to a section of elder-pith impregnated with protein (2 

 per cent 'Deuteroalbumose') x 600. a Remains of nucleus of elder-pith 

 cell before addition of OSO4. b, c, d 4 mins, 14 mins and 60 mins respec- 

 tively after addition of OSO4. From Fischer.^"* 



with blepharoplasts. These are derived from centrosomes, which in 

 Equisetum, for instance (Sharp^i^), appear in the haploid generation 

 for the first time in the early mitoses of the spermatogenous tissue. 

 There is evidence that in many plants these bodies come from inside 

 the nucleus. This subject is reviewed by Yuasa.^^** 



It is abundantly clear that orientating centres within the cell are 

 not all of one kind, nor do they all originate similarly. The non-astral 

 spindle of plants is alone sufficient to demonstrate this fact. A more 

 fundamental question than the morphological status of the centriole is 

 the nature of the orientating process which it induces in the surrounding 

 cytoplasm. This subject is discussed by Swann in a succeeding section. 



no 



