180 Mr Boulenger, On the migration of the thread-cells, etc. 



On the migration of the thread-cells of Moerisia. (Preliminary 

 note.) By C. L. Boulenger, B.A., King's College. 



[Read 22 February 1909.] 



In a recent paper whilst describing the structure of the 

 Egyptian medusa Moerisia lyonsi I called attention to the fact 

 that large nematocysts were constantly to be found among the 

 endoderm cells of the manubrium. Careful examination of a 

 larger series of sections has convinced me that these nematocysts 

 are in process of migration through the tissues, a phenomenon 

 similar to that recently described by Hadzi in hydroids. 



The main thread-cell batteries in Moerisia are those around 

 the oral opening and those on the four perradial tentacles. 



The thread-cells of the oral battery develop in the more 

 proximal parts of the manubrium and make their way through 

 the endoderm and structureless lamella to the ectoderm of the 

 mouth region, the movements being effected by the amoeboid 

 cnidoblasts of the thread-cells. Similarly, the nematocysts of the 

 perradial tentacles are not formed in situ but probably develop 

 in the large ocellar bulbs at the bases of the tentacles. 



