42 THE BIOLOGICAL PROBLEM OF TO-DAY 



small germ-cells afterwards develop into the very 

 different, adult gregarine- cells. 



If the characters of a species be associated with 

 a hereditary mass, an actual substance that is 

 handed on from the parent-cell to the offspring, it is 

 clear that the infusoria-like vagrant young of the 

 Acinetan, and the sickle-shaped embryos of the 

 Gregarine possess it, although for some time they 

 are quite unlike the parent organism. For at last 

 they become an Acinetan or a Gregarine, exactly like 

 the parent- cell from which they arose as embryos. 



These circumstances, among unicellular organ- 

 isms, are a weighty indication of the error of con- 

 cluding, with Weisniann, in the case of multicellular 

 forms, that because cells are unlike in outward 

 appearance, the hereditary mass, or, as I call it, 

 the nuclear matter, within them is also unlike. 

 Such an assumption would involve us in the 

 greatest contradictions. For the supposition that 

 the nucleus is the hereditary mass transmitting 

 the characters of the species necessitates the con- 

 clusion, in the case of unicellular forms, that the 

 hereditary mass remains in possession of all the 

 rudiments of the cell while it passes through the 

 various phases of its cycle of development. Other- 

 wise, these phases would have to be acquired anew 

 in each case. We must, therefore, represent the 

 possibilities of exchange between the nucleus, in its 

 capacity of bearer of the hereditary mass, and the 

 protoplasm as being such that all the rudiments 

 are not simultaneously in activity, but that some of 

 them can remain latent for a time. 



