MICROSCOPICAL TECHNIQUE. 337 



modification in individual cases, but a few experiments will usually 

 enable one to obtain the desired results. . , Complete stupifica- 

 tion of the organism must be produced, so that when it is removed 

 to a killing fluid no contraction will take place. Care should be 

 exercised, however, not to carry on the process too slowly, as 

 maceration may ensue. 



Coekf iterates. — The most beautiful results were obtained with 

 sea-anemones, which ordinarily are so difficult to preserve in a 

 well expanded condition. These were allowed to expand in a dish 

 with as little water as possible. Then crystals of magnesium 

 sulphate were placed in the bottom of the dish and allowed to 

 dissolve slowly until a saturated solution was obtained. The 

 process of dissolving may be hastened, if necessary, by stirring up 

 the water gently from time to time with a pipette. Several hours 

 were required to completely stupefy large specimens. When nar- 

 cotisation was complete, a few crystals placed in the mouth of the 

 sea-anemone had no effect ; but if the process had not gone far 

 enough, the lips of the animal would slowly spread open, and then 

 would follow sometimes a violent contraction of the whole animal. 

 This method was tried upon Metridium marginatum.^ Sagartia 

 leucolena, and Halocampa produda with excellent results, the ten- 

 tacles remaining perfectly expanded after the animals had been 

 transferred to Perenyi's fluid, picro-sulphuric acid, or formalin. 

 The same method applied to Astrangea, Scyphisto?na, and various 

 hydroids did not give as good results as those obtained with the 

 sea-anemones. The polyps were not equally afl'ected, so that only 

 portions of the colonies were perfectly expanded. A large 

 Physalia treated in this way was preserved in 4 per cent, formalin, 

 with all the tentacles and polyps fully extended. 



Echinoderms., — Star-fishes and sea-urchins were killed with the 

 ambulacral feet and pedicellaria well extended, by placing them 

 upon the aboral surface for a short time in a saturated solution of 

 Epsom salts, and then transferring them to 4 per cent, formalin. 

 The epidermis of the star-fishes, however, was rendered soft, and 

 was subsequently easily rubbed ofl", but this was probably due to 

 the formalin. 



Specimens of Synapta were readily preserved without any 

 constriction by very slowly and intermittently adding to the water, 



