No. 2.] THE DEVELOPMENT OF THE NEWT. 29 1 



same animal ; this is stated by Iwakawa ('82) to be the case 

 with Triton pyrrhogaster. These facts incline me strongly 

 towards the view, also taken by Leydig, that the various 

 structures usually grouped together under the name Dotter- 

 kern have nothing but the name in common. 



I have here nothing to say upon the significance to be at- 

 tributed to the curious bodies found in Myriopod and Arachnid 

 eggs, and I cannot attempt to pass upon the peculiar views of 

 Balbiani and Sabatier, but can only repeat that their explana- 

 tions, however valid they may be for these particular groups of 

 animals, are by no means satisfactory if applied to the amphib- 

 ian Dotterkern. 



We can from the nature of the case only surmise as to the 

 physiological meaning of the bodies found in the amphibian 

 egg. It is a seductive hypothesis that the amphibian yolk- 

 nuclei are in some way concerned with the formation of yolk. 

 The number, size, constancy, and complexity of structure of 

 these bodies in the Q%g of the newt, their appearance about 

 the time of beginning yolk-formation, and their disintegration 

 or absorption after yolk-formation is complete, point to them 

 as serving some physiological purpose during the building up 

 of the cell. Whether they are, as Hertwig believes, " peculiar 

 local gatherings of nutrient substances," or whether they are 

 true formative centers, is a difficult question to determine. 

 The fact that they have not been found in all amphibian ova 

 is certainly against regarding them as of high importance, but 

 it is premature to urge an objection based on negative observa- 

 tions. It is possible, and I think probable, that future inves- 

 tigation will show the yolk-nuclei to be of general distribution 

 in all amphibian ova of certain stages of development. It 

 appears to me certain that where the yolk-nuclei do occur they 

 are not mere accidental agglomerations, but have a real physio- 

 logical significance, probably related to the construction of 

 yolk. I am strongly inclined to believe that the yolk-nucleus 

 bears the same relation to the cytoplasm that the nucleoli do 

 to the germinal vesicle. 



Yolk-formation. — The yolk first appears when the ovum has 

 reached a diameter of about .4 to .5 millimeters. A vacuolation 



