CHROMOSOMES AND MITOCHONDRIA 277 
hour stage up to the three-days-nine-hour stage. 
The cells of the earliest stage studied contained mito- 
chondria (Fig. 76) which were differently arranged 
in the germinal layers: the ectoderm and entoderm 
cells contained, for the most part, rods and threads, 
the granules being scarce, and the mesoderm cells 
were characterized by numerous granules and few 
rods and threads. At the three-day stage the mito- 
chondria of the neuroblasts became difficult to 
stain by the usual method, but did stain like neuro- 
fibrils. These and other observations led Meves 
to the conclusion that the mitochondria are of con- 
siderable importance in cellular differentiation and 
are in fact the bearers of hereditary Anlagen. 
Since this paper of Meves appeared, the zodlogical 
periodicals have been flooded with the results of in- 
vestigations of the mitochondria in almost every 
sort of germ and somatic cell, both normal and 
abnormal, and in Protozoa and Mertazoa, In- 
VERTEBRATES and VERTEBRATES. No report on 
spermatogenesis, odgenesis, or early embryonic de- 
velopment is complete without reference to the mito- 
chondria. In plants, also, cellular bodies have been 
described of a mitochondrial nature (Meves, 1904; 
Duesberg and Hoven, 1910; Guilliermond, 1911). 
A large number of new terms have been coined 
for the purpose of describing these cytoplasmic in- 
clusions. Some of them are as follows: (1) mito- 
chondria, applied by Benda (1897, 1898) to certain 
granules with definite staining reactions; (2) chon- 
driosomes, proposed by Meves (1908) for both single 
