BROOKS AND RITTENHOUSE: ON TURRITOPSIS. 439 



manufacture of the yolk granules by the growing ova, except a layer 

 at the outside which is transformed into the epithelium of the ovary. 

 The cells of the ovarian wall are small and somewhat flattened. Their 

 nuclei are of about the same size as the nuclei of the primitive germ 

 cells, but are less dense. The nucleoli are conspicuous and stain 

 deeply. In general the cells of the epithelium of the ovary are similar 

 to the cells in other parts of the ectodermal layer of the subumbrella 

 except that they are not as much flattened. The eggs in the ovary 

 lie next to the mesogloea, that is, there is no ectodermal tissue between 

 them and the supporting layer. The ovarian eggs are irregular in 

 shape due to their being crowded together; but when liberated they 

 become spherical. 



DEHISCENCE. 



The eggs are imbedded in the ectodermal layer of the manubrium. 

 As the ova grow and increase in size the epithelium of the ovary 

 becomes more and more distended. When they have reached maturity 

 the outer ectodermal tissue of the ovary is under considerable tension. 

 Finally, when the time for dehiscence arrives, the outer wall of the 

 ovary is ruptured by the aid of the muscular contractions of the manu- 

 brium and bell, and the eggs escape into the cavity of the umbrella. 

 The process of egg laying is very similar to that described for Stomo- 

 toca. 



The number of eggs deposited by a single female medusa varies 

 considerably. It is usually between twenty and thirty-five. On 

 one occasion an exceptionally large female was taken in the tow; her 

 ovaries were seen to be crowded with eggs. She was put into a sepa- 

 rate dish of sea water for the purpose of counting the number of eggs 

 that she would lay. The next morning at the regular hour the eggs 

 were deposited and the number was found to be fifty-six, which is 

 unusually large. I made many other counts, but this was the only 

 time that the number exceeded fifty. As a rule it is from twenty to 

 thirty-five; only rarely is it as high as fifty. These numbers seem 

 remarkably small when we consider the enormous quantities of eggs 

 that are laid by many of the other animals of the ocean, the numbers 

 often reaching many millions, as among some of the Echinodermata 

 and Mollusca. 



It is a rather curious fact that these animals are always so very 



