March 31, 1898] 



NATURE 



521 



prepared, the muscular structure of the body-wall and the | 

 general internal anatomy are seen to great perfection. 



I have not yet succeeded in preparing specimens of Arenicola 

 when in their patural condition, so as to show their internal 

 structure well, but have made some most excellent preparations 

 by carefully cutting the animal open from end to end, spreading 

 it out on the glass, and displacing the intestine and its append- 

 ages so as to be quite clear of the body, but yet to show the 

 numerous blood-vessels passing to the lateral branchiae from the 

 main trunks along the intestine, which, however, are imperfectly 

 seen in Fig. 2, which I give as an illustration of what may be 

 done by partial dissection. Of their kind no preparations could 

 be more satisfactory than some thus made, since the general 

 anatomy is seen to great perfection, and the colour of the blood 

 has remained unchanged for years, though in other cases, from 

 some unexplained cause, it quickly turned brown. 



It was the desire to preserve some of the beautiful Nudi- 

 branchs that led me to mount animals on slides. The lovely 

 purple Eolis quickly loses its colour in alcohol. It should be 

 killed in dilute alcohol, but kept in it a very short time, and 

 then arranged on the glass and nearly dried. A strong solution 

 of gum should then be placed over it, and the whole kept damp 

 over diluted alcohol, to enable the gum to soak well into the 

 animal, so as to protect the pigment from the balsam, in which 

 it is soluble. I have specimens which have been mounted for 

 more than seven years without showing any further change than 

 the loss of a bluish tint, which occurs almost at once. 



Most excellent transparent slides may be made with the 

 so-called spider crabs, and these sometimes show well the 



Fig. 2. — Arenicola partly dissected. 



manner in which they are covered with a growth of sertularians, 

 sponges, ascidians, &c. The animal is properly arranged on 

 the glass, and at first gentle, and afterwards stronger, pressure 

 applied, using waxed paper and glass covered with flannel ; by 

 which means the whole may be pressed flat without material 

 distortion. The body and legs may indeed be made a little 

 wider than natural, but this is to a great extent counteracted 

 by lateral shrinking. At all events the general results are 

 extremely good, and the muscles in the legs well seen. 



Various species of Mollusca can be prepared so as to show 

 their general anatomy by dissolving away the shell with 

 hydrochloric acid in diluted alcohol. The organic matter of 

 the shell retains the natural form, and shows the attachment of 

 the various parts of the animal, which may be stained or not 

 according to circumstances. Judging from what I have done, 

 it will be possible to prepare instructive slides from the shells 

 alone of some species, by dissolving away the carbonate of lime 

 and mounting the membranous residue, which retains the 

 natural form and much of the colour. 



When first I attempted to mount Medusae as lantern-slides, I 

 looked upon them as most unpromising, and never imagined 

 that it would be possible to prepare such specimens as I now 

 possess. The first step must be to dissolve out all the included 

 salt. For some years I used to put the newly caught specimens 

 of Atirelia into methylic alcohol, diluted with half its bulk of 

 fresh water, and after leaving them in for some hours, with 

 occasional movement so as to prevent adhesion to the glass, 

 they were digested over and over again with fresh diluted 



NO. 1483. VOL. 57] 



alcohol. Specimens so prepared are so colourless and trans* 

 parent that little of the general structure can be seen, but 

 if kept many months in alcohol they turn somewhat brown- 

 yellow and show their structure moderately well. On the 

 whole it is, however, better to stain them. I have experimented 

 with a great variety of colouring-matters, but find that the best 

 are tincture of madder, Beale's carmine, methylene-blue, port 

 wine, and tincture of galls. The canal-system and the general 

 structure are well seen when Beale's carmine is used, but 

 the colour is unnaturally bright, whereas the colour of madder 

 is more in harmony with nature. Methylene-blue gives good 

 results with fresh specimens, but does not stain those which 

 have been kept long in alcohol. 



Though I have many splendid specimens prepared as de- 

 scribed, my last year's experience shows that, at all events for 

 some Medusae, a 4 per cent, solution of formic aldehyde is far 

 better than alcohol. Into this the newly-caught animals were 

 at once put, and it was subsequently used to dissolve cut the 

 salt. The superiority of this over alcohol is that Medusae retain 

 their form almost unaltered, and the most delicate parts can be 

 moved about and arranged without fear of tearing. The only 

 serious objection is that the very delicate fringe of Aurelia may 

 be too rigid to be properly extended. No such objection exists- 

 in the case of Cyaitcea or Clvysaora ; and Cyanaa may be 

 .stained so as to be of nearly the natural colour, which is other- 



FiG. 3.— W«;r//Vi stair.ed with carmine. 



wise lost. In Fig. 3, I give an illustration of an Aurelia stained 

 with carmine when in a 4 per cent, solution of formalin to which 

 a little sulphurous acid was added. 



In mounting Medusae some special methods are necessary. 

 Having removed the salt and stained the specimen as thought 

 desirable, the lantern-slide glass is put into one of the usual 

 developing dishes, and the animal floated out, and to some 

 extent properly arranged, when under the liquid. The specimen 

 may then be half an inch thick in the centre. No attempt 

 should be made to dry it at once, since the greater part of the 

 included liquid usually diffuses out, and nearly the whole can 

 be drained off by keeping the slide inclined and covered up so 

 as not to dry. In some cases the liquid passes oflf badly, but 

 comes off" rapidly, if a solution of gum is spread over the animal. 

 As the edge dries, it should be covered with a strong clear solu- 

 tion of gum to which a little glycerine has been added to make it 

 less brittle when dry, and this process continued until the whole 

 specimen has been covered with gum. It should then be 

 kept for some days in a wet state, so that the gum may soak 

 well in, and any small bubbles not easily removed mechanically 

 may disappear by absorption. At first I used to keep the speci- 

 mens in a developing dish over a little water, covered up with 

 a closely-fitting plate of glass, but sometimes in the course of a 

 single day they became coated with a long growth of mould. 



