96 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



INHERITANCE. 



The doctrine that the mitochondria play a part in the transmission of heredi- 

 tary traits is based upon the necessity of admitting the existence of a cytoplasmic 

 heredity. The claim is based on the well-known experiment of Godlewski, which 

 showed that an egg (deprived of its nucleus) when fertilized with sperm of an- 

 other species retained certain maternal characteristics on development. In fact, 

 there is nothing new in the conception that there is such a thing as cytoplasmic 

 heredity. Jenkinson (1914, p. 152) and Conklin (1915, p. 176) freely admit it. 

 What is new is the view that mitochondria carry it. 



Let us pause a moment in order to consider the claims of the advocates of this 

 view, which was first enunciated by Meves (1908, p. 849), though Van der Stricht 

 also guardedly made reference to the possibility that mitochondria may play a 

 part in heredity in 1908 (p. 4). They do not say or even hint (as the adherents 

 of the chromosome hypothesis have not refrained from doing, in the case of the 

 chromosomes) that the mitochondria constitute in any sense of the term the sole 

 basis of heredity. They believe, however, in general, that the mitochondria play 

 a part in the transmission of those characters which are cytoplasmic. Meves 

 (1908, J). 850) says that the nuclear characters are carried over by the chromosomes, 

 those of the plasma by the chondriosomes. This idea is beautifully supplemented 

 by Meves 's subsidiary hypothesis, according to which the mitochondria are trans- 

 formed into all products of cellular differentiation. In other words, here is a 

 material that can be seen to go through all the stages of development and actually 

 give rise to the peculiar and characteristic differentiations wliich are the hereditarj^ 

 traits. The trouble is that the evidence that the mitochondria play a part in 

 histogenesis (p. 102) is no more convincing than that in favor of the view that they 

 constitute the material basis of heredity. Broman's working hypothesis is that 

 while the chromosomes are the bearers of the hereditarj^ qualities of the race and 

 species, the mitochondria carry those peculiar to the individual. It is interesting 

 to observe that Wilson (1914, p. 352) writes: 



"Genetic experiment has already given some ground for the conclusion that definite 

 types of hereditary distribution may be immediately dependent upon elements containetl 

 in the protoplasm. Recent advances in our knowledge of the 'chondriosomes' or 'plasto- 

 somes' provide this conclusion with at least a possible cytological basis." 



All through the work on heredity, as well as in the other biological problems, 

 the tendency is observed to affix the responsibility for the phenomena to structures 

 with definite form — with each new discovery of a morphological entity to become 

 optimistic and to think that we are well on the road toward a solution of the prob- 

 lem. The basic laws of heredity were appreciated by Mendel long before the dis- 

 covery of the chromosome; yet the chromosomes were seized upon with great 

 avidity. So it is with the mitochondria. 



The adherents of the chromosome hypothesis in this country and elsewhere 

 are naturally opposed to this view that the mitochondria are even partial carriers 

 of heredity. It is said that the cases in which it has been shown that mitochondria 



