NEMATOCYSTS OF MICROSTOMA. 



WM. A. KEENER AND JOHN F. BARKER, 

 UNIVERSITY OF VIRGINIA. 



For a long time the nematocysts of Microstoma were con- 

 sidered to be structures that the worm elaborated as did Hydra. 

 Martin ('08) published an account of the manner in which 

 Hydra is attacked by Microstoma and indicated his conviction 

 that the namatocysts of Microstoma were derived from the 

 Hydras that had been eaten. Kepner (n) published an ac- 

 count of the histological details involved in the process of trans- 

 porting the nematocysts of Hydra from the enteron to the epi- 

 dermis of Microstoma. In this account the inference was made 

 that this complicated series of phenomena must mean that 

 Microstoma handled these nematocysts in this manner in order 

 to use them. This inference was early challenged by Glaser 

 (n). A tentative reply was given Glaser's note in Science, 

 Volume 34, page 213, 1911. 



The details of the processes involved when Microstoma 

 deals with the nematocysts are so vafiable and so intricate that 

 it was felt that these processes could mean only one of two 

 things, namely, either this was a method of eliminating indigestible 

 foreign bodies or a method of securing weapons of defense or 

 perhaps offense. 



From time to time since 1911 efforts have been made to de- 

 termine which of the two meanings was behind this conduct of 

 Microstoma. This paper represents the results of our efforts 

 that have thus extended over a decade and have been taken 

 up each year of this decade to a certain extent. 



MATERIAL AND METHODS. 



Microstoma caudatum is found rather abundantly in the early 

 spring months in the submerged detritus along the banks of 

 fresh water ponds about the University of Virginia. Sometimes 

 Hydras are found living with it in great numbers ; at other times 



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