Evidence from Metazoan Germ-Cells 15 



day. Were their attention called to it they would probably 

 frankly say that they have little interest in f^cnesis in tliis 

 sense. That the sperm here described is not peculiar in 

 every respect to the species Argas minmtus is certain from 

 the meager comparative information we possess, as Casteel 

 has shown. Nevertheless not merely general analogy, but 

 strong indications contained in even the little comparative 

 knowledge w^e have in this particular case, warrant the sup- 

 position that in some respects the sperm of the species would 

 be peculiar to the species, to say nothing of the genus, 

 family and so forth. The development is, consequently, due 

 to heredity, and the cytoplasm is "inheritance material" 

 as ascertained by direct observation. 



Evidence from the Ovum 



We now turn to the ovum to see what can be learned con- 

 cerning hereditary substance in the development of the 

 ovum iself. Attention should be called at the outset to tlie 

 important difference between the sperm and the ovum in 

 the kind of specialization in each. The sperm, it will be 

 noticed, is far more specialized for its own particular life 

 than is the ovum, this "particular life" of the sperm con- 

 sisting in its great power of locomotion. As a consequence 

 of this difference, the ovum as an entity has no such sharp 

 distinction from the ovum as a geiTninal element as has the 

 spermatozoon. This difference is expressed in one way 

 by the assertion that the fertilized ovum is the individual 

 organism in the one-celled stage of its life. No such state- 

 ment is ever heard about the spermatozoon for the obvious 

 reason that the sperm does not transform directly into the 

 embryo as does the egg. From the absence of so distinctive 

 a character of the ovum as such, it happens that tlie hered- 

 ity of the ovum is not so distinguishable from tlie heredity 

 of the organism of whose life it is a stage, as is the case 



