672 SUMMARY OF CURRENT RESEARCHES RELATING TO 



10 parts ; water 60 parts ; acetic acid (2 per cent.) 5 parts. (2) Chrom- 

 acetic Acid : Chromic acid (1 per cent.) 25 parts ; acetic acid (2 per cent.) 

 5 parts ; water 70 parts. 



The eggs are left in one of these fluids twenty-four hours, then washed 

 in distilled water, which should be often changed. The egg-envelopes are 

 next removed by the aid of needles, and the eggs are then ready for 

 surface-study. 



For the purpose of sectioning the eggs are transferred from the water 

 used in washing to 50 per cent, alcohol, then to 70 per cent., 85 per cent., 

 and 95 per cent., leaving them twenty-four hours in each grade. The last 

 grade should be changed several times. The eggs are then clarified in 

 turpentine one to two hours, and then placed in paraffin that melts at 

 50° C. from one-half to one hour. 



Prof. Schultze states that the success of the method depends on follow- 

 ing precisely the directions given as to time. If the eggs remain longer, 

 either in alcohol, turpentine, or paraffin, the results may be entirely un- 

 satisfactory. If the conditions are strictly fuUowed the eggs have the 

 consistency of the paraffin, and cut excellently without crumbling in 

 sections 1/200 mm. thick, 



For staining, borax-carmine was used, directly after washing, twenty- 

 four hours. The eggs were next placed in acid alcohol of 70 per cent, 

 (five drops of the pure acid to 100 ecm. of the alcohol) to remove a part 

 of the colour. 



The first hardening fluid does not penetrate well, and is not well 

 adapted for fixing the central parts of the egg. 



Preparing Eyes of Molluscs and Arthropods.* — Mr. W. Patten's 

 methods for preparing the eyes of Molluscs and Arthropods are as 

 follows : — 



I. Molluscs (preparation of young Pectens from 1-3 mm. long). — 

 (1) Specimens are placed in a mixture of equal parts of sublimate and 

 picrosulphuric acid. After ten or fifteen minutes they are washed in 25 per 

 cent, and 70 per cent, of alcohol. 



(2) The shells are then opened, and the mantles dissected out with 

 needles. Thus treated, the shape of the mantle is well preserved, whereas 

 if removed before hardening it becomes much coiled and twisted. 



(3) Each mantle edge may be cut, according to its size and curvature, 

 into three or four pieces, and these will then lie sufficiently straight for 

 convenient sectioning. 



It is necessary to use a different reagent for nearly every part of the 

 eye. 



The Bods. — Chromic acid gives the most varied results according to the 

 strength, time of action, and temperature of the solution, or by various 

 combinations of these three. For instance, 1/20 to 1/5 per cent, for 

 thirty to forty hours failed to give any conception of the structure of the 

 rods, while other parts of the retina, and of the eye itself, were well pre- 

 served ; but when allowed to act for half an hour at a temperature of from 

 50° to 55° C, perfectly preserved rods with their nervous networks are 

 obtained, whilst, on the other hand, the remaining tissues become so 

 granular and homogeneous as to be unfit for study. This treatment allows 

 the rods to be removed in flakes, and their ends examined without the aid 

 of sections. It is only in this way that the axial nerve-loops can be 

 observed. 



* MT. Zodl. Stat. Ncapel, vi. (1886) pp. 733-S. Cf. Amer. Natural., xxi. (1887) 

 pp. 401-4, ;iU(l this JoumaJ, ante, pp. 53 and 82. 



