370 PRESERVATION OF MARINE ORGANISMS 



depends to a great extent upon the healthy condition 

 of the specimens. Directly the tow net comes on 

 board, the Plankton must be poured into a glass jar, 

 and the jelly-fishes at once picked out by means of 

 a pipette or some other handy instrument, and placed 

 in a glass vessel containing sea water. This glass 

 vessel must be absolutely clean, and free from the 

 slightest trace of chemicals. 



The medusae should be given about half an hour to 

 expand and to recover from the shock. If the medusae 

 after the first half-hour look in a sickly condition, the 

 sooner they are preserved the better ; but if in a healthy 

 condition there is no need to hurry over their pre- 

 servation. They may be left in the vessel for several 

 hours, provided that it is kept in a cool place out of 

 the heat of a summer's sun. 



The simplest and quickest method for preserving 

 either a few specimens or several dozen is by pouring 

 diluted formalin into the sea water. The secret of 

 success depends upon keeping the medusae in motion 

 whilst the formalin is being poured in. First stir the 

 medusae very slowly and very gently round and round 

 with a clean glass rod. When all are in motion, begin 

 pouring in the formalin slowly and gently down the 

 side of the vessel. About 10 c.c. of formalin 10 per 

 cent, may be taken as about the mean quantity to add 

 to 100 c.c. of sea water. An exact quantity is of little 

 importance, and it is better to add too much than too 

 little. 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 well-expanded con- 

 dition. Some species are more liable to contract than 



