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, 
Fic. 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. Fauré-Frémiet 
(1910) describes them in living cells (Fig. 78, D) as 
