804 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
The plan followed by Kuprrer (His and Braune’s Archiv Anat. Abth., 1882), HENNEGUY (Bull. 
de la Soc, Philom., Paris, 1879, pp. 75-77), and others involve too many processes to be adopted when 
the species studied are numerous, and the quantity of material is large. 
Various circumstances conduce to render Teleostean eggs difficult objects for treatment—not 
only on account of their small size, pelagic ova being rarely more than a millimetre in diameter— 
but the tough nature of the capsule and fluidity of the contents render the removal of the former a 
most delicate and hazardous task. If hardened before the capsule is removed, shrinking results ; 
and if the capsule be removed before hardening, the egg is more or less disorganised, unless the 
operator be very fortunate. The best sections are those gained by leaving the egg almost intact, 
and by hardening, staining, and imbedding in toto, but this plan is beset by many dangers. On 
removing the egg from the sea-water, and reference is made here to marine ova solely, the capsule 
is carefully pierced in order to facilitate the admission of the various media into which it is to be 
transferred. Save for this puncture, the egg is left entire, and thus it is passed through all the 
processes of killing, hardening, staining, clearing, and imbedding. 
The paraffin method proved to be the only practical one, other methods, such as imbedding 
in pith, which might serve for large eggs, such as those of the Salmonide, were unsuitable 
for eggs so small and frail as those of the Gadoids, Plewronectide, &c.* Various forms of the 
microtome were used in preparing the extensive series of sections of the various Teleosteans 
considered in these pages—the rocking microtome of the Cambridge Scientific Instrument Company 
being found very useful. The large Caldwell microtome, used in the classes of zoology at the 
United College, and kindly lent by the authorities of the University of St Andrews, was of great 
service; while the Jung (Thoma’s) microtome was found to be well adapted for older stages of the 
embryos, and for adult ovaries—a series of sections being eut by Dr Scuarrr. The sweeping 
motion of the last-named instrument proved very efficient in cutting through the more mature 
skeletal and other tissues of young fishes, to which task the fixed razor of the English microtomes 
proved unequal—refusing, in fact, to pass through the firm connective and cartilaginous elements. 
Il. Kiniie, Frxine, anp Harpentnc—Corrosive Sublimate.-—The saturated solution is one of 
the most efficient killing and fixing fluids available in the laboratory, and it kills, fixes, and hardens 
so rapidly that Teleostean ova require to be left in it for a very short time. As soon as the 
penetration of the fluid is complete, they are removed and washed in dilute alcohol, rather than in 
distilled water, Washing must be well done, in order to prevent subsequent deposition of crystals 
in the tissues. The desirability of staining, clearing, and cutting after treatment with this fluid is 
too well known to require any explanation—the best preparations being found to be those in 
which, after killing and fixing, the subsequent operations are immediately proceeded with. A mix- 
ture of two parts corrosive sublimate and one part acetic acid was found to be most serviceable. It 
is a powerful killing and fixing fluid, and produces the best results. For killing, two or three 
minutes usually suffice, and washing is then done in very weak alecohol—the alcohol being 
frequently changed until the killing medium is wholly extracted, and graduated alcohols follow, 
viz., 30, 40, 50, and 60 per cent. 
Picro-sulphurie Acid (KLEINENBERG). This useful killing and fixing fluid does not produce 
the best results, since it frequently causes the blastomeres in early stages to expand and burst the 
capsule, thus entirely disorganising the embryonic structures. WHITMAN experienced the same 
results (op. cit., p. 152), but occasionally this effect is not produced, and, if successfully killed and 
hardened in this fluid, ova are often found to produce most satisfactory sections. It is, however, not 
reliable. Creosote is added on KLEINENBERG’S suggestion, but apparently without much effect. If the 
ova placed in picro-sulphurie acid maintain their normal shape, they remain four or five hours, and 
then are transferred into 70 per cent. alcohol, which is frequently changed, as it becomes stained by 
the yellow picrie acid. When the alcohol is seen to be uncoloured, the ova are then ready to 
be transferred to absolute alcohol, preparatory to clearing. Emery recommends this fluid for 
* Hennecovy used elder-pith soaked in alcohol and covered with a layer of collodion. 
