252 WM. A. KEPNER AND JOHN Fi BARKER. 



EXPLANATION OF FIGURES. 

 PLATE I. 



FIG. i. A Microstoma slowly moving amid the bases of the tentacles of 

 Hydra. X 50. 



FIG. 2. In response to the presence of Microstoma the Hydra has spread 

 its expanding peristome along ventral surface of Microstoma. X 50. 



FIG. 3. The expanding peristome has glided posteriority and dorsally, in 

 direction indicated by arrow in Fig. 2, over surface of Microstoma as the 

 Hydra flexed its body and pressed the Microstoma between its greatly ex- 

 panded peristome and its bent body. From this embrace the Microstoma 

 escaped. X 50. 



FIG. 4. Soon after this escape the Microstoma returned to be captured by 

 the tentacles of Hydra. After the inception of ingestion the tentacles of 

 Hydra were bent back so as to lie almost parallel to the axis of the polyp. 

 The ingestion was a slow process. X 50. 



FIG. 5. Shows the manner in which a Microstoma was held by a Hydra. 

 The Microstoma slowly glided out of this embrace between the ends of the 

 tentacles. X 50. 



FIG. 6. When the Microstoma had escaped it showed two wounded regions 

 one bearing two nematocysts and the other three nematocysts. These 

 nematocysts were at first embedded so that only their poison-sacs projected 

 from the surface of the Microstoma. Very early a mass of mucus formed in 

 each wounded region. The lateral mass moved posteriorly (as shown by 

 arrow) and fused with the posterior one. As these masses of mucus grew in 

 length, they dragged the five stinging threads from the body of the Micro- 

 stoma. The combined mass of mucus, containing five nematocysts, eventually 

 was cast off. After this the Microstoma moved about normally. X 50. 



FIG. 7. Shows a dividing Microstoma with a maximum charge of nemato- 

 cysts at its surface. When the nematocysts are this frequent the Microstoma 

 is said to be " loaded." X 50. 



