tological purposes; besides, the removal of the osmic acid leaves the animal in a good condition for staining.

Dr. Mayer's experience with Sapphirina appears to support him. in the following conclusions in regard to the nature of the action of osmic acid, viz., that the hardening effect of the acid is due to the formation of inorganic precipitates within the tissues. This is made evident by the fact that the animal becomes soft and flexible as soon as these precipitates are removed by bleaching.

This method of bleaching has been used by Dr. Mayer for removing natural pigment. Alcoholic preparations of the eye of Mysis, for instance, can be fully bleached in toto, but with better success by operating with single sections. To avoid swelling, which is apt to arise by the use of aqueous fluids, staining media of an alcoholic nature should be used.

6. Chromic Acid.-Chromic solutions have in common with osmic acid, the peculiarity of hardening by virtue of the chemical combinations which they form with cell-substances, and all the consequent disadvantages with respect to staining. The use of chromic acid in the Zoological Station of Naples may be said to have been largely superceded by picro-sulphuric acid, corrosive sublimate and Merkel's fluid, for it is now seldom used except in combination with other fluids. It is sometimes mixed with Kleinenberg's fluid, for example, when a higher degree of hardening is required than can be obtained by the use of the latter fluid alone. It is a common error to use too strong solutions of chromic acid, and to allow them to act too long. Good results are in some cases obtained when the objects are treated with a weak solution (1⁄2-1⁄2 per cent.) and removed soon after they are completely dead.

Professor Merkel, who employed a mixture of these two solutions in equal parts for the retina, states that he allowed from

1Dr. Pfitzner ("Morph. Jahrb.," B. xvII, p. 731, 1882) has recently made use of chromic acid followed by (1) osmic acid, or by (2) chloride of gold, formic acid and safranin (or hæmatoxylin) for the demonstration of nerve-terminations.

Flemming (see his method on a following page) believes that chromic acid is one of the most reliable fixing reagents for the karyakinetic figures, and has proved that objects hardened in this acid can be beautifully and durably stained.

2" Ueber die Macula lutea des Menschen," &c., Leipzig, 1870, p. 19.

three to four days for the action of the fluid. Dr. Eisig has used this fluid with great success in preparing the delicate lateral organs of the Capitellidæ for sections, and recommends it strongly for other annelids. Dr. Eisig allows objects to remain 3-5 hours in the fluid, then transfers to 70 per cent. alcohol. With small leeches I have found one hour quite sufficient, and transfer to 50 per cent. alcohol.

8. Corrosive Sublimate.-Prompted by a statement found in an old paper by Blanchard,' Dr. Lang began experimenting with corrosive sublimate as a medium for killing marine Planarians, and his marked success led him and others to employ the same with other animals. In most cases Dr. Lang now uses a saturated solution of corrosive sublimate in water. A saturated solution in picro-sulphuric acid, which in some cases gives better results if a little acetic acid (5 per cent. or less) is added, is also used Blanchard's mode of treatment was to mix a quantity of the aqueous solution with the sea water, and thus poison the animals. Dr. Lang, on the contrary, removes the sea water so far as possible before applying the solution. With Planarians he proceeds in the following manner:

The animal is laid on its back and the water removed with a pipette, the solution being then poured over it, it dies quickly and remains fully extended. After half an hour it is washed by placing it in water and changing the water several times during thirty minutes. It is next passed through 50 per cent., 70 per cent., 90 per cent. and 100 per cent. alcohol. In two days it is fully hardened, and should then be stained and imbedded in paraffin as early as possible, as it is liable to become brittle if left long in alcohol. The time required by the corrosive sublimate varies with different objects, according to size and the character of the tissues. As a general rule, it may be said that objects should be removed from the fluid as soon as they have become thoroughly

1" Recherches sur l'Organisation des Vers," by Emile Blanchard. Ann. des Sci. Nat. Zool. Ser. 3, t. VIII, 1847, p. 247.

2 These solutions given in Zoolog. Anzeiger, 1879, 11, p. 46.

The original solution (Zoolog. Anzeiger, 1878, 1, p. 14-15), now little used, stood thus:

saturated by it. In order to kill more quickly than can sometimes be done at the ordinary temperature, the solution is heated, and in very difficult cases may be used boiling.

Corrosive sublimate has been used with success by Dr. Lang and others in the following cases: Hydroids, corals, Nemertines, Gephyrea, Balanoglossus, Echinoderms, Sagitta, Annelids, Rhabdocela, Dendrocœla, Cestodes, Trematodes, embryos and adult tissues of Vertebrates and, according to Mayer and Giesbrecht, Crustacea with thin chitinous envelopes, e. g., Sapphirina, Copepods and larvæ of Decapods.

The two great advantages of Dr. Lang's method are, (1) that animals so treated are easily stained, and (2) they are killed so quickly that they are left, in most cases, in a fully extended condition. Hot corrosive sublimate kills leeches so instantaneously that they often remain in the attitude assumed the moment before the fluid is poured over them. The color, however, is not so well preserved as when killed with alcohol, or even with weak chromic acid.

It should be remembered that objects lying in a solution of corrosive sublimate must not be touched with iron or steel instruments; wood, glass or platinum may be used.

9. Dr. Andres' Methods of treating Actinia.-Among the various methods employed by Dr. Andres in killing the Actiniæ, thé three following, given in the order of their excellence, are said to have worked most satisfactorily:

A. Corrosive sublimate.-With small animals a hot solution, used in the manner recommended by Dr. Lang, gives good results; with larger animals, where this mode of treatment fails, the fluid. must be injected. The cannula of a glass syringe, filled with the hot fluid, is inserted into the mouth at the moment it opens, which act habitually follows on gently touching the lip. After injecting, the hot solution is poured into the glass containing the animal and a small quantity of sea water.1

If the operation is cleverly performed, the animal remains fully expanded, as the mechanical pressure of the injected fluid prevents contraction.

After from five to fifteen minutes the animal is washed in distilled water and allowed to remain twelve hours in 50 per cent.

1 Andres.

"Intorno all'Edwardsia Claparedii,” in the Proceedings of the "Reale Accademia dei Lincei," Vol. v, Ser. 3, Mar. 7, 1880, p. 9.

alcohol, then passed through the higher grades of alcohol. Borax-carmine and hæmatoxylin used for staining.

This mixture, poured very slowly into the containing glass, often gives very good results, both for anatomical and histological purposes.

C. Nicotine and Tobacco Smoke.-a. A solution of nicotine (I g.) in sea water (1 1.), conducted into the vessel containing the animal fully expanded in a half liter of sea water, by means of a thread sufficiently large to empty the flask holding the nicotine solution in the course of twelve hours.

b. The vessel containing the animal in an extended condition, covered by a bell jar in which tobacco smoke is confined, until the animal becomes completely benunibed.

After being deprived of sensibility by either of these methods, the creature may be killed in corrosive sublimate, or in picro⚫ sulphuric acid.

D. Dr. Andres finds that in the use of chloroform, dropped slowly into the water, or administered in form of vapor, maceration usually sets in before the power of contracting is lost. Good preparations of the internal parts may be obtained by injecting a weak solution of osmic acid. The method of freezing has also been employed with some success. For this purpose three vessels are placed one within the other, the central one containing the actinia, the middle one ice and salt, and the outer one cotton. The ice containing the congealed animal is dissolved in alcohol or an acid.

E. Maceration.-It is often important to see the cells of a tissue in situ before freeing them with needles. In such cases Dr. Andres proceeds as follows:

1. Killed with corrosive sublimate.

2. Left in 25 per cent. alcohol twenty-four hours.

3. Soaked for a short time in a very thin solution of gum arabic, then in a somewhat thicker solution, and finally imbedded in a very thick solution.

4. Hardened in 90 per cent. alcohol.

5. Thick sections prepared for dissection with needles. The sections are placed on a slide in water, which dissolves the gum.

(To be continued.)

1 A little camphor (1 ccm. to 100 ccm.) added to the alcohol will facilitate the removal of the sublimate.

2 This method originated with Salvatore Lobianco.

NOTES ON THE HABITS OF THE "SAVANNAH CRICKET FROG."

ONE

BY CHARLES C. ABBOTT.

of the earliest indications of returning spring is the clear, bell-like note of the little batrachian, called by many the "Savannah cricket," known in New Jersey as the "peeper," and scientifically designated Acris crepitans Baird.

Abundant as is this batrachian, but little seems to be known of its habits, and certain misstatements concerning them have been long in print, and have never, that I am aware, been either questioned or contradicted.

During the month of April, 1881, I had excellent opportunities for observing these little creatures, and finding that but little had been recorded concerning them, availed myself of my chance, and watched them closely for several weeks.

While a network of ditches in a low meadow were being repaired and cleaned, I followed the workmen closely, for the purpose of gathering any novelties that might be thrown out with the mud and dead leaves that had accumulated in the ditchbottoms. Much of interest was found, particularly a number of the rare "Muhlenberg" turtles; but the one striking feature of the locality, at this time, was the wonderful abundance of little "rattlers" (Acris crepitans), as I prefer to call them. They were in full song, and when not disturbed, made more noise than all the frogs in the neighborhood together. They were quite timid, however, and on being approached were straightway "mum." Their vocal efforts seemed to increase until about May 1st, when their eggs were deposited in little masses, attached to the blades of coarse grass. I did not succeed in following the various stages of developmental growth from the egg to the matured animal, but was enabled to determine that it was more protracted than in the case of the common tree-toad (Hyla versicolor). The difference is, I believe, quite seven weeks.

To return to the adult "peepers." From the date of their earliest appearance until May 20, their numbers were incalculable. In every portion of the meadows at all wet, they were to be seen. Extremely active and very shy, they were difficult to catch, provided you pursued a single individual, but by sweeping an ordinary dip net along the grass at the edge of any little pool, sev