Evidence from Somatic Hist ogene sis 37 



with which this particular ontogeny disposes of the mitochondria! 

 hypothesis of heredity so far as this case is concerned. 



Recurrence to the description and figures (42 a, b, c, d, e, f ) will 

 recall that the mitochondria, widely distributed through the cyto- 

 plasm in the early spermatocyte (?HZ.) assemble into a rather 

 sharply defined ring-shaped mass (m.r., figure 42b) as the cell 

 transformation proceeds., and finally take a position in the devel- 

 oping sperm about as remote as they can get from some of the 

 most actively and fundamentally changing parts of the organism. 

 (mi. f figures 42 e, f, g). 



There is no more possibility of explaining the development of 

 many of the parts of this sperm, the outer sheath, for example 

 (o.t., figures S6e and f ) as due to the influence of the mitochondria 

 than as due to the influence of the nucleus. And I point out 

 again for the hundredth time what the real issue is here. The 

 observations certainly do not exclude the possibility that the 

 mitochondria exercise some invisible influence on the development 

 of, say, the outer sheath. There may be or there may not be such 

 an influence. But the observations do show conclusively that 

 cytoplasmic portions of the cell other than mitochondria are 

 operative in producing the outer sheath. 



It should be said in concluding this reference to the sperm of 

 the chicken tick that Casteel finds the mitochondria located finally 

 in the end of the sperm opposite that which contains the nucleus ; 

 and that this end goes ahead in locomotion, the motion being pro- 

 duced by a circlet of mobile processes at this end. From this he 

 believes that the contractile elements are mitochondrial in origin. 

 The conjecture that the mitochondria of the spermatocyte take 

 part in producing the motor elements of the sperm tail is perhaps 

 strengthened by the observations of other students, notably Lewis 

 and Robertson. These investigators were able to follow the mito- 

 chondria in the ontogeny of the living sperm directly into the 

 tail, where they transform into two equal threads situated along- 

 side the axial filament. 



The Mitocliondrial Theory Tested by Histogenesis 



If this hypothesis that mitochondria in developing sperm 

 cells give rise to the motion-producing structures of the 

 sperm tail, then the mitochondria would be genuine "inheri- 

 tance material" for these particular elements, the hereditari- 



