168 ME. E. T. BEOWNE — BISCATAN PLANKTON : 



lies in the manner in whicli this is done. The strength of the formalin should be about 

 5 to 10 per cent. (5 per cent, solution containing 5 cc. of formaldehyde, 40 per cent, 

 strength, and 95 cc. of water — either fresh water or sea-water may be used). The 

 quantity of formalin to be poured into the vessel containing the medusae depends upon 

 the quantity of sea-water in that vessel ; it is better to add too much than too little. 

 About 10 cc. of formalin may be taken as about the mean quantity to add to 100 cc. of 

 sea- water. 



The secret of success depends upon keeping the medusae in motion ■whilst the formalin 

 is being poured in. Eirst stir the medusae very slowly and vei-y gently round and 

 round with a clean glass rod. When all are in motion then begin pouring in the 

 formalin slowly and gently down the side of the vessel. Keep the medusae in motion 

 whilst the formalin is being added, and for at least two minutes after. The stirring is 

 very important, as it produces an even distribution of the formalin in the sea- water, and 

 the motion keeps the medusae off the bottom and allows them to die in a fairly good 

 expanded condition. 



The medusae may be left at the bottom of the vessel for a few hours, and then they 

 must be transferred to a stronger solution of formalin. I store my specimens in a 

 10 per cent, solution of formalin, and change it at least once before finally sealing the 

 bottle. Another method is to pour a small quantity of 20 per cent, formalin, or even a 

 few drops of formaldehyde, into the bottle before finally storing it away. I firmly 

 believe in using plenty of formalin, as I have often found medusae in a state of 

 maceration when only very weak solutions have been used. 



The method of simply adding formalin to the sea-water and giving a gentle stir round 

 is the quickest and easiest method for killing medusae. It gives fairly good results with 

 all kinds of medusae, but some species are more liable to contract than others. The 

 results are usually better when the medusae are in a fairly quiescent condition than 

 when they are vigorously swimming about. 



Cocaine and Formalin. — To obtain medusae in a nice state of expansion and with the 

 tentacles stretched out it is necessary to use an anaesthetic. This gives a little extra 

 trouble, but the results are well worth the trouble when really nice specimens are 

 wanted. The aniEsthetic which I use is hydrochlorate of cocaine (soluble in water), in 

 a 1 per cent, or 2 per cent, solution, either in fresh water or in sea- water. As only a 

 very small quantity is used at one time, a bottle containing 100 cc. lasts a long time. 

 It is best to place the medusae in a glass vessel with just sufficient sea-water for them to 

 swim in. Add a little cocaine (about 3 cc. of 1 per cent, cocaine for every 100 cc. of 

 sea-water) and stir gently with a glass rod to mix the cocaine with the sea-water. If 

 the medusae at the end of about 10 to 15 minutes have their tentacles expanded and they 

 do not contract when touched with the glass rod no more cocaine need be added ; but if 

 still active, add a little more cocaine and repeat the stirring process. It is better to add 

 about half the cocaine at first, and gradiially increase the quantity, than to give the 

 whole dose at once. An overdose usually causes a prolonged contraction. "When the 

 medusae are anaesthetized stir them gently round and pour in the formalin solution. 

 Keep on stirring whilst the formalin is being added, and for a minute or longer after. 



