STRUCTURE OF THE LARVA OF SPONGILLA LACUSTRIS. 439 



weak solution of borax carmine and subsequently washed with 

 spirit and acid, being left in both of these liquids for about 

 fifteen minutes. They were usually left in the spirit and acid 

 for the same time as they were left in the borax carmine solu- 

 tion, but the specimens on the cover-slips had to be left in 

 longer, as they were to be examined whole. They were after- 

 wards treated with 90 per cent, alcohol, in which they were 

 kept to await further treatment. 



The specimens on the glass cover-slips, which were to be 

 examined whole, were further stained with a weak solution 

 of bleu de Lyon in 90 per cent, alcohol. To guard against 

 overstaining they were taken out from time to time and exa- 

 mined, and when sufficiently stained they were passed through 

 absolute alcohol, cleared in pure xylol, and finally mounted 

 between two cover-slips in Canada balsam dissolved in xylol. 

 Being thus mounted they could be examined from both sur- 

 faces. 



{b) Corrosive Sublimate and Glacial Acetic Acid. — 

 This mixture was made up of four parts saturated solution of 

 corrosive sublimate in 90 per cent, alcohol and one part glacial 

 acetic. The specimens were left in this fluid until they became 

 whitish in colour, and were afterwards treated in essentially 

 the same way as those preserved in absolute alcohol. 



(c) Flemming's Weak Solution. — The specimens were 

 left in this fluid for about ten minutes, and were then washed 

 in a current of water for an hour and finally brought up through 

 the alcohols into 90 per cent., in which they were left to await 

 further treatment. 



(d) Perenyi's Fluid. — The specimens were left in this 

 fluid for an hour and were then transferred into 70 per cent, 

 alcohol, in which they remained for two hours, at the end of 

 which they were removed into 90 per cent., which was changed 

 several times during the subsequent twenty-four hours. 



(e) Osmic Vapour and Miiller's Fluid. — The specimens 

 were held in the vapour given off from a 2 per cent, solution 

 of osmic acid. The bottle which contained the solution was 

 previously warmed. They were afterwards placed in Miiller's 



