BROOKS AND RITTENHOUSE: ON TURRITOPSIS. 441 



the time of spawning the next morning, which took place at the fixed 

 period. 



THE EGG. 



The egg of Turritopsis is spherical and devoid of a membrane when 

 first laid, and none is subsequently formed. In size it is very small 

 and may easily be overlooked. If the water is free from sediment 

 and the dish containing the eggs is placed upon a piece of black paper, 

 the eggs are visible to the naked eye. They measure 0.116 of a milli- 

 meter in diameter. They are among the smaller of the medusan eggs. 

 MetschnikofF gives the measurements of the ova of 19 species of 

 medusae. The sizes range from 0.024 mm. to 1.5 mm. Cunina 

 proboscidea has the smallest and Poly.renia albescens the largest egg 

 of the species included in his list. The egg of Turritopsis is just 

 slightly larger than that of Rathkca fa.ciculata according to the meas- 

 urement of MetschnikofF. 



In the substance of the egg two parts are distinguishable: an outer 

 layer of clearer ectoplasm which consists of viscid formative yolk 

 composed of protoplasm with very fine granules; and a central mass 

 of entoplasm which is dense and opaque and filled with large, dark 

 granules of nutritive yolk. From the fact that the entoplasm is crowded 

 with these coarse dense granules of nutritive material, the egg is very 

 opaque and the germinal vesicle is not to be seen from the exterior. 

 Thus the changes which take place during maturation and fertilization, 

 and the nuclear phenomena of segmentation, as well as the formation 

 of the entoderm cannot be followed in the living egg. For this reason 

 the egg of Turritopsis is not as suitable for study during life as are 

 the beautifully transparent eggs of Liriope and Eutima for instance, 

 which allow all the changes that take place within the egg during 

 development to be followed easily. 



The specific gravity of the eggs is greater than that of seawater and 

 consequently they sink to the bottom of the aquarium as soon as they 

 are discharged from the cavity of the umbrella. In opacity the egg 

 of Turritopsis is intermediate between the esg of Stomofora rugosa, 

 which is extremely dense and of a chalky white color, and the egg of 

 Stomofora apicata which is semi-transparent and appears bluish white 

 by reflected light. In color the egg of Turritopsis is yellowish white. 





