MEDUSA OF MICROHTDRA RYDERI. 645 



Fig. 3. — The central portion of a very young tentacle of the medusa of 

 Limnocodium. Drawn for comparison with fig. 2. X 500. 



Fig. 4. — A group of three nematocysts in the tentacle of the medusa of 

 Microhydra. X 1000. 



Fig. 5. — Nematocysts from the tentacle of Limnocodium. x 1000. 



Postscript. — The writing of this paper has led me to 

 commence investigations on the methods of asexual repro- 

 duction amongst Hydroids, and the work is now being carried 

 on in the Marine Laboratory at Plymouth. I have found 

 AUman's " Schizocladium ramosum" and have observed 

 the formation of fission-frustules, their liberation, and subse- 

 quent development. My observations completely confirm 

 those made by Allman. 



The ffustule when nipped off consists of a thin, transparent 

 layer of ectoderm with nematocysts, a thick layer of endoderm 

 loaded with granules, and a hollow central cavity. The bud 

 which is detached from the hydroid phase of Microhydra 

 (Potts, PI. 36, figs. 17 and 24) is exactly like the fission- 

 frustule of Schizocladium, both in shape and structure. 



Hincks' suggestion that Schizocladium is probably an 

 Obelia has turned out to be correct. Some of the colonies 

 have liberated Medusa which belong to the genus Obelia. 



I have also found aClava-like hydroid detaching numerous 

 fission-frustules from its hydrorhiza. These buds drop to the 

 bottom of the aquarium and lightly attach themselves by one 

 end to the glass. They are now a week old and have not yet 

 begun to develop. 



Nov. 4th, 1906. 



VOL. 50, PART 4. NEW SERIES. 46 



