FOR ZOOI.OGICAI, I'URI'OSRS. 121 



Sponges. — To preserve specimens of these merely as museum 

 specimens it is not necessary to subject them to previous preparation, 

 but merely to place them in 70 per cent, alcohol, changing the same 

 several times in order that the specimen may be completely pene- 

 trated by it. 



To prepare dried specimens, wash them first in fresh water for 

 about two hours, then leave them for a day in strong ordinary 

 alcohol, and afterwards dry them in the open air or in the sun. 



Anthozoa. — The two principal divisions of this group are the 

 Octactiniffi or Alcyouaria, and the Hexactinite, of which the Sea- 

 anemones are the most familiar representatives. 



Alcyonium dtgitatum, sometimes known as " Dead men's fingers," 

 is very common on the British coasts, but it is difficult to preserve 

 specimens with the polypes well expanded. The method to be 

 employed is as follows : Place the specimen in clean sea-water until 

 it is completely expanded, for which one may have to wait a day or 

 two. The vessel used must be only large enough to contain the 

 specimen, and when it is expanded the quantity of sea water must be 

 reduced by means of a siphon until only enough is left to cover the 

 specimen. Then a mixture is made of acetic acid (pure), 100 parts, 

 chromic acid (i per cent, solution) 10 parts, and a quantity of this 

 mixture twice as great as that of the water containing the specimen 

 is rapidly poured over the latter. The polypes are thus killed before 

 they can contract. The specimen is removed after a few seconds 

 into dilute alcohol of 30 per cent, whence it is transferred into 

 alcohol of increasing strengths successively until it is in 70 per 

 cent. A saturated solution of corrosive sublimate, made hot, may 

 also be used in the same way. 



Peniiatula and Gorgonia may be killed in a similar manner ; or 

 the former may be taken suddenly when expanded from the sea 

 water and plunged into the fixing liquid. 



Actiniaria. — Sea-anemones are perhaps the most difficult of all 

 marine animals to prepare either for exhibition or for study. They 

 are extremely sensitive and very muscular, and the density of the 

 tissues is such that it is very difficult to kill or paralyse the muscles 

 before they contract, or to anaesthetize the sensory tissues com- 

 pletely. It often happens that when the operator believes a specimen 

 is killed or rendered insensible in the expanded condition, and 

 transfers it to some other reagent, it begins to contract violently, ami 



