27O GEO. W. TANNREUTHER. 



the nature of chitin. When it is nearly formed, a second or inner 

 membrane begins as a secretion from the ectodermal cells over 

 the entire embryo just beneath the outer egg membrane (Figs. 

 25 and 26). 



According to Kleinenberg, the entire primitive ectoderm is 

 used in the formation of the outer and inner membranes. The 

 formation of these membranes in Hydra sp.? confirms Brauer's 

 account in that the inner ends of the ectodermal cells persist and 

 become the definitive ectoderm. 



After the membranes are formed, the eggs are glued to the 

 object on which the parent rests. This, however, is not always 

 true. In a few instances observed, the embryo hatched out while 

 the eggs were yet attached to the parent'. Brauer states that the 

 eggs are glued by a sticky secretion from the ectoderm to the 

 object on which the parent rests, and that the parent remains in 

 contact with the egg until the embryo hatches out. 



The formation of the interstitial cells and of the body cavity 

 was not studied. The embryo hatches out in from eight to ten 

 days after the outer and inner membranes are formed. 



General Remarks. 



The condition necessary for the appearance of sexual organs 

 in hydra has long been a question of much interest, especially 

 among scientific investigators. Various chemical solutions as 

 well as different conditions of food and temperature have been 

 tried with little or no success. 



Downing (2) by subjecting hydra to various degrees of reduced 

 temperature was able to get hydra to produce sexual organs after 

 an exposure in a dark refrigerator to a temperature of about 12° 

 C. for twelve hours. But as sexual organs appeared at the same 

 time on several control hydras in the laboratory which were kept 

 in the light at the temperature of the room, he concluded that 

 light and temperature are not controlling factors in determining 

 the appearance of sexual organs. 



During the three different years that Hydra sp.? were collected 

 at intervals from two to three times a week, no sexual organs 

 were found, but buds were abundant in the winter season as well 

 as during- the warmer months. From this I was led to infer that 



