146 



BERTRAM G. SMITH 



occurring in eggs of Amblystoma tigrinum fertilized under nat- 

 ural conditions; the material secured for the further investigation 

 of this subject has not yet been worked up. Polyspermy seems to 

 be characteristic of heavily yolk-laden eggs lacking a preformed 

 micropyle. 











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49 



50 



Fig. 49 Meridional section through an egg of Cryptobranchus allegheniensis, 

 killed 12 hours after fertilization, showing fusion of germ-nuclei. The sperm- 

 nucleus is probably the smaller one. X 240. 



Fig. 50 Meridional section showing fusion of germ-nuclei in another egg killed 

 12 hours after fertilization. The sperm-nucleus is probably the lower and smaller 

 one. X 240. For the position of this copulation-nucleus in the blastodisc see fig. 

 52 which is drawn from the same section. 



3. Union of the germ-nuclei, and formation of the first cleavage 



spindle 



In two eggs killed twelve hours after fertilization, the germ- 

 nuclei have been found in the process of uniting (figs. 49 and 50) ; 

 in these two cases the copulation-nuclei are at approximately the 

 same distance from the surface (see fig. 52), quite deeply situated 

 in the blastodisc and a little to one side of the axis of polarity. 

 The smaller germ-nucleus is probably the sperm-nucleus. The 

 egg-nucleus stains brilliantly with borax-carmine; the sperm- 

 nucleus takes the stain less deeply. The sperm-nucleus especially 

 is surrounded with dense cytoplasm; in one case (fig. 50) this 



