OBSERVATIONS ON HYDRA 603 



plasm of the egg, it may go on much as described above 

 (Text-fig. 2, h, 1), or the cytoplasm may, to all appearance, be 

 absorbed directly into that of the egg and the nucleus alone 

 undergo visible change. Wager (13) describes such degenerative 

 products formed from whole cells, from nuclei, and from 

 nucleoli. I have not seen any of the last named in process of 

 formation, but from the small size of some of the masses it 

 seems probable that this is the case in my specimens also. 

 In several cases a nucleolus seemed to be breaking through the 

 nuclear membrane of an interstitial cell. 



These degenerative cells are looked on as stores of energy 

 to be used up by the embryo during development. Tann- 

 reuther (11) states that they divide by amitosis after their 

 absorption into the egg-cell, but I have seen no signs of this. 

 It has been stated that they are all used up before the young 

 Hydra hatches, but this is not the case, for large numbers 

 are present in the tissues of newly hatched Hydras and they 

 do not entirely vanish till some time after hatching. 



In my specimens the egg-shell is formed by a kind of vacuole 

 formation at the surface of the egg. The edges of the vacuoles 

 come in contact with one another, and their limiting membranes 

 then harden to form the spicules. This is in accordance with 

 the observations of Brauer (2) and Kleinenberg (7). The eggs 

 then drop off and fall to the bottom. 



Nematocysts. 



The nematocysts have been much studied, and of late 

 have been used largely to distinguish the different species of 

 Hydra. There are four main types of nematocyst, large 

 pear-shaped, small pear-shaped, and two types of cylindrical 

 nematocysts^ which differ from each other in size and in the 

 way the thread is coiled inside. As the two last are not always 

 strictly cylindrical, and as the names in other respects are not 

 suitable, Schulze (9) has proposed to name the different types 

 from their functions as Penetrant, Volvent, and Glutinant. 

 Otto van Toppe (12) was the first to study the functions of all 

 three types in detail. 



