Martin, A Note on the Occurrence of Neraatocysts and Similar Structures etc. 261 



(4) Microstomum obtained from Scotch lochs at a depth beyond 

 the region in which Hydra occurred were found to be free from 

 Nematocysts. It is possible that this form had been previously 

 described as a separate species under the name of Microstomum 

 inerme. 



(5) The Nematocysts in Microstomum are found lying in vacuoles 

 under the skin and no trace of a Nematoblast cell can be dis- 

 covered in the sections. The Nematocysts usually lie singly in the 

 vacuoles, but in some instances vacuoles have been found contain- 

 ing three to four Nematocysts, and in 

 these cases the Nematocysts may be of 

 more than one type. 



(6) Some Microstomum had been 

 fed at 1 o'clock on Hydra stained inten- 

 sely with Methylene blue. At 6 o'clock 

 one of the Microstomum had a mass of 

 blue material in its gut. Next day the 

 colour had unfortunately faded during 



Va. 



Vb. 



the process of digestion, and only in one case was a Microstomum 

 seen with the blue Nematocysts of the stained Hydra on which 

 it had fed under the skin. 



The instances of the occurrence of Nematocysts in Microstomum 

 (jiganteum and papillosum have been dealt with in the paper referred 

 to above. In May 1908 I found a Microstomtitn, rubromaculatum 

 on some weed to which was attached some colonies of Obelia. The 

 Microstomum contained oval Nematocysts in packets of 3 4 under 

 the skin, and singly in the gut. These Nematocysts emitted a 

 thread on explosion, and appeared identical with the Nematocysts 

 of Obelia. In the case of Stenostoma sieboldii I was able to infect 

 the forms which I found at Naples with the Nematocysts of 

 Eudendrium, 



