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spherical shape and finely granular appearance. The daughter nuclei multiply by division. While these changes occur, the whole cell or spermatocyst becomes greatly elongated. At the completion of this stage, the parent nucleus at the inner end of the cell disappears, and a nucleus similar in appearance appears at the outer end, f. It is probable, but not demonstrated, that the two nuclei are identical, in other words, that the parent nucleus

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FIG. 8.-Development of the spermatozoa in sharks, after Semper. migrates from one end to the other. The upper nucleus henceforth is passive, remaining behind to degenerate after the spermatozoa have been discharged from the cyst. Each one of the daughter nuclei, after subdividing still further so as to become very small, g, gathers a distinct mass of protoplasm around itself, and becomes a spermatoblast. The further development proceeds by alteration of the shape of these bodies: the nucleus elongates, becomes S-shaped, h. The elongation advances, the nuclei become straight and rod-like, and lie parallel to one another in the upper end of the cell, i. If we look at the cells from the outer surface of the ampulla, the center of the end of each cell is occupied by a cluster of dots corresponding to the bundle of rod-like nuclei seen endwise, m. Each long nucleus forms a spermatozoon head, which is connected with a thread-like tail. The development is completed by the discharge of the bundle of spermatozoa, leaving the large nucleus behind.

The essential feature of this whole history is, that a cell with a

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single nucleus divides to form a compound body in which there is one large element with one kind of nucleus and numerous small elements, all with nuclei similar among themselves, but different from the single larger nucleus. The same thing occurs when the egg sensu stricto, or the thelyblast, is developed. In the case of the egg, it is the larger element which is preserved as the female part; in the case of the spermatocyst, it is the smaller elements which are preserved as the male parts. The two processes are complementary.

These facts have led to the following hypothesis of the relation of cells to the sexual elements. In an ordinary cell the two elements are intimately united in a latent condition, so that an ordinary cell is hermaphrodite or neuter, sexless, by which I mean it has no sexual differentiation. Diagrammatically this condition may be represented by Fig. 9, A. To form an egg the male portion is removed in several parts, which are the polar globules, while one large portion becomes the egg or thelyblast, Fig. 9, B. To form the spermatozoa, the two elements separate, the mother nucleus, or female part, remains behind, and if my hypothesis is correct, it, as well as the egg, must be called a thelyblast; the spermatozoa are discharged, and are capable of further vitality. They are the homologues of the polar globules. For both structures the common name arsenoblast has been suggested. If the above hypothesis is valid, then there is a fundamental distinction between cells on the one hand, and the genoblasts (the sexual products) on the other— every genoblast contains. only one sexual element,

A

B C

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FIG. 9.-Diagrams to show the relation of the sexual products to cells. A, an ordinary cell; B, egg with polar globules; C, spermatocyst with

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every cell contains both. When sexual reproduction occurs, a thelyblast from one source unites with an arsenoblast from another source-the two by their fusion complete a perfect cell, which is called the impregnated ovum. In the next article this process will be described.

In conclusion I wish to repeat that the conception of sex here advanced is only an hypothesis, which further research may cast aside, but which I hope may be confirmed, because it is already possible to bring forward many strong arguments in its favor.

For the convenience of those who may wish to pursue these subjects further, I quote below some of the principal articles, especially those which contain further bibliographical references :

A. ON THE STRUCTURE OF CELLS AND NUCLEI.

1. Max Schultze. Das Protoplasma der Rhizopoden und der Pflanzenzellen. Ein Beitrag zur Theorie der Zelle. Leipzig, 1863.

2. W. Kühne. Untersuchungen ueber das Protoplasma und die Contractilität. Leipzig, 1864.

3. Heitzmann. Untersuchungen ueber das Protoplasma. Sitz. berichte Akad. Wiss. Wien. 1873,

Abth.

4. R. Hertwig. Beiträge zur einheitlichen Auffassung der verschiedenen Kernformen. Morph. Jahrb. 11 (1876), p. 63.

5. Eimer. Weitere Nachrichten über den Bau des Zell-kernes. Arch. für mikros. Anat., XIV, 94.

6. Flemming. Zur Kenntniss der Zelle und ihrer Theilungserscheinungen. Arch. f. mikros. Anat. Bd. XVI, p. 248.

7. Klein. Observations on cells and nuclei.

Part 1.—Quar. Journ. Micros. Science, XVIII (1878), p. 375.

Part II.-Quir. Journ. Micros. Science, XIX (1879), p. 129.

B. ON THE CELLULAR NATURE OF PROTOZOA.

8. Schulze, F. E. Rhizopoden Studien.

Archiv. f. mikros. Anat., IX, ; X, 328; XI, 94.

9. Hertwig, R. Ueber Podophrya gemmipara, nebst Bemerkungen zum Bau und · zur Systematischen Stellung der Acineten. Morph. Jahrb., 1, p. 20 (1875).

10. Bütschli. No. 18, below.

II. Bütschli. Ueber den Dendrocometes paradoxus, Stein, etc. Zeit. f. wiss. Zoöl., XXVIII, 49 (1877).

12. Bütschli. Beitrage zur Ventniss der Flagellaten und einiger verwandten Organismen. Zeit. f. wiss. Zool., XXX, 205 (1878).

13. Zeller. Untersuchungen ueber die Fortpflanzung und die Entwickelung der in unseren Batrachiern schmarotzenden Opalinen. Zeit. wiss. Zoöl., XXIX, 352 (1877).

14. Hertwig, R. Der Organismus der Radiolarien. Jena. Denksch., I, 129. 15. Vignal. Recherches histologiques et physiologiques sur les Noctiluques. Arch. Physiol. norm. pathol. 2me Ser., T. V., p. 415. (Paris, 1878.)

C. ON THE DEVELOPMENT AND STRUCTURE OF EGGS, AND THE PHENOMENA OF IMPREGNATION.

16. Van Beneden, Edouard. Recherches sur la composition et signification de l'Oeuf. Mém. Cour. Acad, R. Belg., xxxiv, p. 1 (1870).

17. Ludwig, H. Ueber die Eibildung im Thierreiche. Arbeiten. Zool. zoot. Inst. Würzburg. Herausgegeben von C. Semper. Bd. 1, p. 287 (1874). (An exhaustive and extremely valuable summary.)

18. Bütschli. Studien ueber die ersten Entwickelungsvorgänge der Eizelle die Zelltheilung, und die Conjugation der Infusorien. Abh. Senkberg. Nat. forsch. Ges., X, p. 213 (1876).

19. Hertwig, Oscar. Beiträge zur Kenntniss der Bildung, Befrüchtung und Theilung des thierischen Eies.

Ister Theil. Morph. Jahrb. I, p. 437.

2ter Theil. Morph. Jahrb. III, p. 1.

3ter Theil. Morph. Jahrb. IV, p. 177.

20. Fol, H. Recherches sur la fécondation et le commencement de l'hénogénie. Mém. Soc. phys. Génève, XXVI, p. 89.

21. Balfour gives a summary of the researches on the maturation and impregnation of the ovum. Quar. Journ. Micros. Sci., XVII (1878), p. 109.

22. Calberla. Der Befrüchtungsvorgang beim Ei von Petromyzon planeri. Zeitsch. f. wiss. Zool., xxx (1878), 437.

23. Kupffer u. Benecke. Der Vorgang der Befrüchtung am Ei der Neunauge. Königsberg, 1878, 4to.

D. ON THE DEVELOPMENT AND STRUCTURE OF SPERMATOZOA.

24. Leydig. Lehrbuch der Histologie (1857), p. 532-537.

25. v. la Valette St. George. In Stricker's Handbuch der Lehre von den Geweben. Cap. XXI, p. 522.

26. Semper. Das Urogenital system der Plagiostomen und seine Bedentung für das der übrigen Sängethiere. Arbeiten. Zool. zootom. Inst. Bd. 11. 1875. Enstehung. Wachsthum und Veränderung der Hodenfollikel, p. 252.

27. Spengel. Arbeit. Zool. zootom. Inst. Bd. 111, p. 1.

28. Sertoli. Sulla struttura di canalicoli seminiferi dei Testicoli, etc.

le scienze mediche, 11 (1877), p. 107.

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29. Gibbes. On the structure of the Vertebrate Spermatozoön. Quar. Jour. Micros. Sci. (1879), p. 487.

30. Weissmann, Samen und Begattung der Daphnoiden. Zeitsch. fur, wiss. Zool. Bd. xxxIII, p. 55.

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THE CONVOLUTION OF THE TRACHEA IN THE SANDHILL AND WHOOPING CRANES.

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BY THOMAS S. ROBERTS.

is well known to ornithologists, that in many birds there are various peculiar modifications of the trachea, or windpipe, which, it is supposed, serve the purpose of adding some particular quality to the voice. Passing by the numerous minor instances of this structure as seen frequently in ducks, in some geese and a few other birds, we find it most strikingly exhibited among the cranes and swans. In certain species of these two groups the trachea enters the enlarged and excavated keel of the sternum, and after a number of convolutions, varying in position and extent with the species, passes out at the place of entrance and thence into the lungs. In such cases, at least, it is plainly great strength and volume of tone which are imparted, as is clearly evidenced by the powerful utterances for which these birds are noted.

It is the present purpose to speak of this point of structure only as it exists in the two American species of cranes, Grus americana and Grus canadensis, with special attention called to its presence in the latter.

That the trachea is remarkably convoluted within the sternum. in the whooping crane (G. americana) has been pointed out and fully described by Dr. Elliott Coues, in his " Birds of the Northwest." But the mistake is there made of stating (on the evidence of others, I believe) that in the sandhill crane (G. canadensis) the trachea is simple; and this supposed entire difference between the two species is presented as strong anatomical evidence of their distinctness.

The fact is, however, that the trachea is convoluted within the keel in the sternum in G. canadensis as well as in G. americana. This I have determined by the examination of four sterna of canadensis, three of which were prepared by myself from birds positively identified as canadensis by the generally recognized external characters. Two sterna of americana have been examined: one the same that was described by Dr. Coues, and with which I have had the opportunity of comparing specimens through the courtesy of Dr. R. O. Sweeny, president of the St. Paul Academy of Natural Sciences; the other a specimen recently prepared by Mr. Wm. Howling, taxidermist, of Minneapolis, Minn., and in whose collection I saw the adult bird from which it was taken. One side of the keel was neatly cut away by Mr. Howling, at my suggestion, and the specimen freely offered for use in the present connection. It is identical in structure with the St. Paul specimen, and is the one from which the drawing has been made.

Although there is not such a radical difference as supposed by Dr. Coues, yet the two species are distinct in respect to their tracheal and sternal development. A glance at the drawings will show this at once. They are alike in so far as the trachea enters the sternal keel in each. But in canadensis the whole sternum is smaller and less stoutly developed; the coils of the windpipe are confined to the anterior half of the keel, and it is this portion alone. that is enlarged; there are only about eight inches (average of four specimens) of windpipe in the keel, to twenty-seven inches (average of two specimens) in americana; the walls of the sternal cavity are much more imperfectly ossified than in americana, where they are everywhere on the outside dense, hard bone. On

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