2 So JORDAN. [Vol. VIII. 



I may add that Gage has appended to his paper an annotated 

 bibliography that must win the gratitude of future students of 

 the natural history of the newt. 



II. Maturation of the Ovum. 



The phenomena of maturation may be taken in their broadest 

 sense to include all the progressive changes in the ovum from 

 its youth up, and cannot strictly be limited to the nuclear 

 changes immediately preceding fertilization. Indeed one may 

 hold with some reason that the early stages of oogenesis are no 

 less significant than the later. 



In amphibian ova two general stages of development may 

 conveniently be distinguished : the early, constructive, or as 

 it may be called, anabolic period, during which the yolk is 

 elaborated and the full size of the ovum reached ; and a second 

 period, beginning with the remarkable regressive metamor- 

 phosis of the germinal vesicle, and culminating in the expul- 

 sion of the polar bodies. The accumulation of yolk may be 

 considered quite as essential to "ripeness" as the extrusion of 

 nuclear substance, since, so far as we know, both are invariable 

 preliminaries to the normal union of male and female pronuclei. 

 It is a fact especially worthy of notice that the germinal vesicle 

 undergoes a progressive development up to the time when yolk- 

 formation is practically completed, and only then begins to show 

 signs of degenerative change ; this significant fact must be 

 taken into account in all conjectures as to the functional role 

 of the amphibian egg-nucleus. 



The maturation phenomena in amphibian ova have been so 

 often and so thoroughly studied, that, where my observations 

 are in full harmony with those of my predecessors, I shall 

 either refrain from all reference to the fact, or shall content 

 myself with bare mention of it without entering into superfluous 

 details. 



Technique. — I have found the two most satisfactory killing 

 agents for the ovarian eggs to be hot water (80° C), and 

 Flemming's chrom-aceto-osmic mixtures. In my experience I 

 have found no advantage in leaving the eggs longer than two 

 hours in Flemming's mixture, and though I have used a solu- 



