Nos. 455-456.] 



FASCIOLARIA. 



in both of them mitosis has been replaced by amitosis through 

 the influence of an extraorchnary circumstance, cold weather or 

 ether. We know of no parallel to the case of the food-ova 

 among the gasteropods. In the trematodes the yolk cells of 

 the egg are perhaps somewhat similar; their nuclei do not divide 

 at all. 



The nuclei of the young endoderm are also out of the ordinary 

 course. We should expect them to divide by mitosis. While 

 in a small percentage of cases they do divide in that manner, 

 in most cases the inchcations are strongly in favor of amitosis. 

 Here neither senescence nor metabolism can be the cause of the 

 amitosis. The cells have not yet arrived at their definitive 

 form, much less become old, and secretion has not yet com- 

 menced ; but, on the contrary, the cells are actively multiplying, 

 so that they quite contradict the theory proposed by Ziegler and 

 vom Rath. 



We see, then, that while the amitosis of Fasciolaria can be 

 attributed to senescence in one case, it cannot be attributed to 

 either senescence or metabolism in the other two cases ; and in 

 the endoderm the amitosis is even regenerative. We ha\e seen 

 that senescence and metabolism cannot be regarded as causes 



Fresnel, Meves and Pfeffer. Upon the hypothesis that miio^i. 

 a 1 t are inde{)endent and non-related processes, cases 

 of this sort are wholly unintelhgible, and consequently indicate 

 a defect in the hypothesis, if not that it is erroneous. It is 

 true that we do not find intermediate modes of nuclear di\ ision 

 between mitosis and amitosis, and yet a priori we shtnild sup- 

 pose them to be related and mitosis to have been derived trom 

 amitosis. The exceptions that are being found arc ah ot them 

 cases in which mitosis would be looked for and amitosis is 

 found. The frequency of mitosis in eml.)ryonic ti>Mie does not 

 prove that embryonic tissue cannot mu]tii)ly by amitosis ; it 

 only shows that there is some reason why in most ca^cs it does 

 not. Since mitosis is such a delicately adjusted and compli- 

 cated process, may we not suppose that a nucleus to be capable 

 of it should be in the best possible condition, — that is, young 

 and vigorous, — and to that end that the surrounding conditions 



