2/O BERTRAM G. SMITH. 



EXPLANATION OF PLATE I. 



Cryptobranchtts allegheniensis. 



FIG. i. Portion of a meridional section of a fertilized egg, showing the meeting 

 of the sperm-nucleus and the egg-nucleus. Each germ-nucleus extends through 

 four sections, of which an inner one is shown in the figure. The section passes 

 midway between the two asters, which lie on opposite sides of the nuclei in a line 

 at right angles to the plane of the section. The egg was fixed with bichromate- 

 acetic formalin and stained with borax-carmine Lyons-blue picric-acid. X 400. 



FIG. 2. Meridional section of an egg killed twenty-two and one half hours 

 after fertilization, showing the resting germ-nuclei. Each germ-nucleus extends 

 through five sections, of which the middle one is here shown. The section passes 

 midway between the two asters, which lie close to the apposed surfaces of the two 

 nuclei in a line oblique to the plane of the section. Fixed with bichromate-acetic- 

 formalin; stained with borax-carmine Lyons-blue picric-acid. X 400. 



FIG. 3. Horizontal section through the resting germ-nuclei of an egg killed 

 twenty-one and one half hours after fertilization. Nearly half of each nucleus is 

 left in an adjacent section. Two asters are shown in the figure. Fixed with 

 bichromate-acetic-formalin; stained with borax-carmine Lyons-blue picric-acid. 

 X 400. 



FIG. 4. Horizontal section through the resting germ-nuclei of an egg killed 

 twenty-two and three fourths hours after fertilization. Each germ-nucleus extends 

 through three sections, of which the middle one is here shown. Two asters are 

 shown in the figure. Bichromate-acetic-formalin fixation; stained with borax- 

 carmine Lyons-blue picric-acid. X 400. 



