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 
proboseidea has the smallest and Polyxenia albescens the largest egg 
of the species included in his list. The egg of Turritopsis is just 
slightly larger than that of Rathkea fasciculata 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 egg of Stomotoea rugosa, 
which is extremely dense and of a chalky white color, and the egg of 
Stomotoea apicata which is semi-transparent and appears bluish white 
by reflected light. In color the egg of Turritopsis is yellowish white. 
