affine itself, is an operation which may, in many cases, be readily accomplished by employing any one of the ordinary intermedia, such as oil of cloves, bergamot oil, creosote, turpentine, chloroform, &c. But with tender objects, particularly those with larger or smaller internal cavities, the process is often attended with great difficulties, and in such cases collapse and shriveling can only be avoided by giving the most careful attention to every step in the process. Dr. Giesbrecht recommends, for difficult cases, chloroform,' as it is one of the best, and at the same time the most volatile solvent of paraffine. (2) Transferring from Chloroform to Paraffine. After the objects have become thoroughly saturated with chloroform, the containing tube is placed on a water bath and heated to about 50° C. the melting point of paraffine; then a small piece of paraffine is added and allowed to dissolve, and this is repeated until bubbles cease to rise from the objects. To make sure that the chloroform has been fully expelled, the objects may next be transferred to pure paraffine and left for a few minutes before imbedding.2 (3) Shellac as an aid in Mounting.-The use of shellac for fixing sections on the slide, introduced by Dr. Giesbrecht, is a very valuable addition to histological methods. By this method hundreds of small sections may be arranged in serial order, and all inclosed in balsam under the same cover without danger of disarrangement. The method is further extremely useful in mounting larger sections, particularly those composed of loose parts, or parts liable to swim apart. 1 Bütschli (Biolog. Centralblatt, B. 1, p. 591) has also recommended chloroform, entirely overlooking, as it would seem, Dr. Giesbrecht's prior publication. For the Hydrozoa, Professor Weismann prefers turpentine to chloroform, as where the latter has been used, the paraffine is liable to be more or less spongy in consequence of bubbles lodged in the tissues. Turpentine renders objects brittle, and on this account chloroform will, in many cases give better results. The spongy state of the paraffine results from the fact that the chloroform has not been allowed to wholly escape. In the case of the Actiniæ, Dr. Andres employs a mixture of turpentine, creosote and alcohol, using successively mixtures containing more turpentine and less alcohol, thus: Giesbrecht. "Methode zur Anfertigung von Serien-Praparaten," in Mitthei lungen a. d. Zoolog. Station zu Neapel, 1881, p. 184. The shellac is prepared and used in the following manner : One part of bleached shellac' mixed with ten parts absolute alcohol, and filtered. The object glass is first warmed to about 50° C., and then a thin film of the shellac is laid on by a glass rod drawn once over its surface. Before using, the slide is again warmed, and the shellac surface washed with oil of cloves for the purpose of softening it. The wash is made with a small brush drawn back and forth until the entire surface has been moderately but evenly wet with the oil. Sections are now cut and arranged for the first cover; this done, the slide is warmed over a spirit lamp so that the paraffine adhering to the sections melts and flows together, forming an even layer which cools almost instantly, and thus secures the position of the sections while those of the second cover are prepared. The sections for the last cover having been completed, the slide is warmed for ten minutes on a water bath, in order that the sections may sink into the shellac and become fixed, and the clove oil evaporate. After allowing the slide to cool the process is concluded by washing away the paraffine with turpentine, and inclosing in balsam dissolved in chloroform.3 'Dr. Mark informs me that he uses "the bleached shellac in the form in which it is prepared for artists as a fixative' for charcoal pictures. It is perfectly transpa rent, and a film of it cannot be detected unless the surface is scratched." Dr. Mark attaches a small label to the corner of the slide, which serves for the number of the slide and the order of the sections, and at the same time marks the shellac side (otherwise not distinguishable). 2 The same temperature is used throughout the operation. 8 Since the above was written, my attention has been called to the following mode of fixing sections, first described by Dr. Gaule (Archiv. f. Anat. u. Phys., 1881, Phys. Abthlg., p. 156): 1. Sections cut dry and placed on the slide in the order and position in which they are to be mounted. 2. They are then smoothed out by the aid of a fine brush wet in 50-60 per cent. alcohol, until all wrinkles are removed and every part is in close contact with the slide. 3. Slide allowed to stand several hours (or over night) until the alcohol has completely evaporated, and the sections are left adhering quite firmly to the glass. The process may be hastened by gently warming to 45-50° C. 4. The paraffine may be removed by any of the solvents in common use, but Dr. Gaule recommends Xylol. A few drops are allowed to flow over the sections, and • after a few moments the paraffine is fully dissolved. 5. The balsam (a mixture of balsam and xylol in equal parts) is placed on the cover-glass, and this allowed to sink slowly, from one side, over the sections. Dr. Gaule finds it convenient, especially with serial sections, to use large coverglasses often nearly as large as the slide itself. Thus a single slide may often contain a large number of sections closely arranged under one cover. For large sections this method offers one important advantage over that of Dr. Giesbrecht; for by the former all wrinkles may be removed, while by the latter the sections must lie as they fall. In the case of smaller sections, not liable to get wrinkled during the placing, I prefer the shellac method. WATER BATH. The diagram represents a convenient form of water bath, devised by Dr. Mayer. It is a small brass box 18cm long, 9cm wide and 8cm high. The tube a, through, which the water is received, and the rod b serve as handles. The receiving tube is closed by a cork provided with a glass tube for the escape of steam, which is bent in the form of a siphon to protect against dust. One and a-half centimeters from the base of the box is an oven (0) .7cm high, and 12cm long, which passes completely through the box, and serves for warming the slides when shellac is used. Above are seen two circular basin-like pits (p) 5.5cm in diam., and 4cm deep, for receiving the two tin paraffine holders. These are covered by circular plates of glass. There are also six tubular pits, one for a thermometer (t), the others for glass tubes. This water bath will be found useful for other purposes than those of imbedding and mounting. It will of course be understood that the purpose in giving its exact dimensions is simply to furnish a guide where one is required. There are at least two important advantages offered by this water bath over those in general use, viz., the slides are protected from dust, and the paraffine is not exposed to the water. :0: ON THE HOMOLOGIES OF THE CRUSTACEAN LIMB. BY A. S. PACKARD, JR. THE trations-Messrs. Sinclair & Son having, at their own expense, kindly struck off an edition of the accompanying plates from the drawings on stone made by them for the Survey. The reader is supposed to have a general knowledge of Crustacea, especially the Phyllopods, a brief account of which may be found in the author's Zoology, where the genera here referred to are figured. As to the anatomy of these interesting Crusta FIG. 1.-Limnetis brevifrons, enlarged. Burgess, del. cea, a transverse section of the anterior part of the body of any genus of Phyllopods (see Pl. x11, Fig. 2, also Fig. 1 in text) will convey an excellent idea of the leading features in their organization, especially those by which they differ from the members of other Crustacean orders. The leading topographical features in the body, particularly of Arthropods, are the form of the elemental segments with their appendages, and the relations of the principal anatomical systems to the body-walls. General relations of the systems of organs to the body walls.We will first look at a section of a typical Phyllopod, such as Apus (Fig. 2). The body-walls are rather thick and the muscles are well developed, particularly the dorsal extensor muscles, and the motor or extensor muscles of the limbs, which arise in part from the dorsal region, and in part from the sides and sternal region. The body cavity is rather small. The heart is large, either cylindrical as in Estheria, or flattened as in Thamnocephalus. The digestive tract is large, capacious, and the cavity of the head is mainly filled with the two liver masses; the brain being remarkably small, while the nervous cord, especially the second and succeeding ganglia, are remarkably small and weak, compared with other Crustacea, either the malacostracous or the entomostracous orders; this peculiarity is well brought out in the transverse sections, where the diminutive gill. Ex fb ht 4 -int noteworthy. The apparent bulk of the body is largely due to the large size and nature of the leaf-like or foliaceous appendages, with their broad attachments; the latter peculiarity is characteristic of the Branchiopods in general and the Phyllopods especially, and is quite different from the definite, small coxal articulations of the legs of Malacostraca or Copepoda. The ovaries or testes, according to the sex, form a large lobulated mass extending along each side of the digestive canal, as far forward as the base of the head. Their relations in Apus are seen in Plate XXII, Fig. 2, and in Thamnocephalus in Plate XIV, Fig. 4 of our essay. 5 en FIG. 2.-Section of Apus ; ht, heart; int, intestine; "g, ganglion; c, carapace; 1-6, the six exites, I being the gnathobase; gill and fb, flagellum, representing the exites. The segments of the body.-Phyllopoda are exceptional to other Crustacea in having an indefinite number of segments composing the body, and in having in one family (Apodida) more than one pair of appendages to an arthromere. While the normal number in the Decapoda is twenty-one, in the Phyllopods it varies from seventeen in Limnetis to forty-seven in Apus. The following table shows the number in different genera of American species: |