66 PETER OKKELBERG 



this respect they seem to behave hke zymogen granules in gland 

 cells. In the resting gland cells the zymogen granules are very 

 abundant, but in a cell which is secreting they decrease in num- 

 ber and size, and may disappear entirely if activity continue. 



Most of the mitochondria in the germ cells of the lamprey are 

 spherical, but occasionally rod-shaped ones may also occur. 

 The theory that the early germ cells may be distinguished from 

 the somatic cells by the shape of the mitochondria has been 

 developed by Rubaschkin ('10) for mammals, Tschaschkin ('10) 

 for birds, and Aunap ('13) for fishes. These investigators think 

 that the mitochondria of the germ cells are spherical, and that 

 during the process of development of the embryo they become 

 chain-like and finally rod-shaped in the differentiated tissue cells. 

 Ihe primitive character of the germ cells is, therefore, according 

 to these investigators, indicated by the fact that they possess 

 granular mitochondria after the other cells of the embryo show 

 rod-shaped ones. That this is a universal character of the early 

 germ cells has been denied by von Berenberg-Gossler ('12) and 

 others. Von Berenberg-Gossler found that in the individual germ 

 cells of the duck and the chick, the shape of the mitochondria 

 may vary from granular and chain-shaped to rod-shaped. Firket 

 ('14) also found that in the germ cells of the chick, the shape of 

 the mitochondria is not constant. 



In the oocyte of the lamprey the mitochondria may be found 

 again after the beginning of the growth period. They are cyto- 

 plasmic structures and not related to the chromidia which are so 

 abundant in the growing oocytes of the various stages. This is 

 in agreement with Schaxel ('10, '11) and others who consider the 

 chromidia to be of nuclear origin and the mitochodria to be of 

 cytoplasmic derivation. 



Meves ('08), the first to study the mitochondria in embryonic 

 cells, upheld the theory which had previously been advanced by 

 Benda ('03) and others, that the mitochondria are bearers of 

 cytoplasmic heredity. This theory has since been advocated 

 by Duesberg ('08, '10) and others. Those who adhere strictly 

 to the chrortiosome theory of inheritance are opposed to it. Ac- 

 cording to Cowdry ('16), the chemical nature of the mitochondria 



