280 



GERM-CELL CYCLE IN ANIMALS 



which mitochondria are supposed to give rise are 

 neurofibrils and myofibrils. Meves (1907, 1908) 

 considered it probable that neurofibrids were trans- 

 formed chondriosomes, and Hoven (1910) seemed to 

 have proved it, but Marcora (1911) and Cowdry 

 (1914) find that the neurofibrils arise independently, 





^ 



^yJi. 



A B C 



Fig. 77. — Mitochondria in the cells of a plant, Pisum sativum. 

 A. Young germ cell. B. Young germ cell dividing. C. Old cell 

 containing vacuoles. {From Duesberg and Hoven, 1910.) 



although mitochondria are present in the nerve 

 cells. Duesberg (1910) is quite positive that the 

 myofibrils of striated muscle fibers are produced 

 by the metamorphosis of chondriosomes from em- 

 bryonic muscle cells, and has recently (Duesberg, 

 1913) strengthened his position by the discovery 

 that the myoplasm described by Conklin (1905) 

 in the egg of the Ascidian, Cynthia, is well supplied 

 with chondriosomes. 



Mitochondrial structures have been studied in 

 both living and preserved cells. Faure-Fremiet 

 (1910) describes them in living cells (Fig. 78, D) as 



