PROCEEDINGS OF SOCIETIES. 57 



QuEKETT Microscopical Club, 



April 24tli.— Ordinary Meeting. Dr. Eobert Braithwaite, F.L.S., 

 President, in the chair. 



After the formal business was concluded, a paper by Mr. G. J. 

 Burch, " How to make Thin Covering-glass," was read. 



The mode adopted was to seal up the end of a glass tube of about 

 ^-inch bore with the blowjnpe, soften it in the flame, then remove it, 

 and blow through it as strongly as possible, so as to form a large 

 and very thin bubble ; this was to be broken and the pieces cut to 

 shape with a writing diamond. If required flat, a piece could be 

 placed on a perfectly flat piece of platinum foil, and dejiressed for a 

 moment into the Bunsen flame. In this way Mr. Burch produced 

 glass 2 dVo^^i ^^ ^^ inch in thickness. 



Mr. Ingpen read a paper " On a False-light Excluder for Micro- 

 scopical Objectives." This consisted of a cap, having a perforation 

 a little larger than the field of view of the objective ; when this was 

 slipped on close up to the front lens, it diminished the angle of aper- 

 ture ; but when brought into contact with the covering glass, it allowed 

 the full angle to be used ; while in either case no rays but " image- 

 forming rays" were admitted, and the milkiness caused by stray light 

 was completely got rid of. This method occurred to Mr. Ingpen upon 

 reading Mr. Wenham's letter in the March number of the ' Monthly 

 Microscopical Journal,' describing his mode of measuring the true 

 angle of a ToUes' ^th objective. 



A paper by Mr. James Fullagar, " On the Development of Hydra 

 vulgaris from Ova," was read, and illustrated with several beautifully 

 executed drawings of Hydra in its various stages. Hydra vulgaris 

 differed in several respects from Hydra viridis ; the egg being larger, 

 and studded with what appeared to be short sj)ines, and surrouuded 

 with a gelatinous envelope, which it retained to the time of hatching. 

 The development of a single ovum was traced from the time of its 

 extrusion. After about fifty-five days a protuberance appeared, a 

 slight rupture was seen in the shell, and a portion of the Hydra 

 slowly emerged. In about two hours rudiments of tentacles appeared 

 as rounded lumps, and in twelve hours the Hydra was fully developed, 

 with seven tentacles, being however still attached to the inside of the 

 shell by the suctorial disk at the posterior end of the body. After a 

 time, varying from twelve to sixty hours, the Hydra finally quitted 

 the egg, and fixed itself to the weed or the side of the aquarium. 

 The growth of the Hydra was very slow, and it could not be observed 

 to feed. After a month, some small entomostraca were put into the 

 cell, which were seized, but not absorbed ; these, however, died from 

 the effects of the stinging power of the tentacles. The ova were not 

 easily found, after extrusion, their gelatinous envelope speedily be- 

 coming covered with extraneous particles. After the extrusion of the 

 ovum, the parent Hydra gradually diminished, and in about twenty- 

 one days the whole body dissolved. The sperm cells continued to dis- 

 charge spermatozoa into the water for some days after the separation 

 of the ovum. The ovisac and sperm cells were generally found on the 



