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tively slender, this condition being especially marked in the region of the kidney. The cellular enlargements of the sympathetic cord in connection with the nerves now may be called ganglia, and the constricted portions between the nerves, which are becoming distinctly fibrous in structure, may be called commissures.

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Fig. 11.—Diagrammatic reconstruction of the sympathetic nervous system of a 21 mm. toad. Reference marks, same as in previous figures. X 24.

Condition after the Metamorphosis.—By the time the tail has almost disappeared, the sympathetic cord not only is completely separated from its antecedent structures, but is removed dorsally and somewhat laterally from the aorta. In the mid-trunk region, it lies as high as the upper border of the notochord (Fig. 12, Sy. G. 2.), while in the preceding stage it was on a level with the lower border of it.

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Fig. 12.-Transverse section through the second spinal nerve, from a toad in which the tail has almost completely disappeared. Col. Sy., collateral sympathetic. R., ramus. Sp. G. 2., ganglion second spinal nerve. Sp. N. 2., second spinal nerve. Other abbreviations, same as in preceding figures. For development of ramus, cf. Fig. 4. X 246. Camera lucida. Reichert, oc. 4, obj. 3.

The ridge and the structure with which it was connected, have now atrophied almost completely. Nearly all of the rami communicantes have become much longer, and the collateral sympathetic also is well developed (Fig. 12, Col. Sy.), while the differentiation of ganglia and commissures is now almost complete.


(1) In the region between the vagus ganglion and the second spinal nerve, the sympathetic arises in a comparatively simple and direct manner : cells, probably of epiblastic origin, scattered in the mesoblast gradually become aggregated (Fig. 2, Sy.) to form a cellular cord. This is similar to the process in mammals described by PATERSON, except that he finds the cord is at first entirely independent of any other structure, while in the toad the cells of the sympathetic cord lie in contact with the fibers of the first and second spinal nerves, from the earliest stages.

(2) In the region posterior to the second spinal nerve, the origin of the sympathetic system is more complex. It appears first as a small ridge of cells (Fig. 1, Ri.) lying close along side the aorta. The cells at the top of this ridge, as it becomes higher, are differentiated to form the sympathetic cord (Fig's. 5 and 6, Ri, and Sy.). Later, the ridge disappears entirely, leaving the cord free, save its connections with the collateral sympathetic and with the spinal nerves (Fig. 12, Col. Sy. and R.).

(3) The sympathetic ganglia and commissures arise directly from the sympathetic cord. The latter becomes enlarged in the region of the nerves, forming the ganglia, while the portions between the nerves become reduced, forming commissures, which, immediately after metamorphosis, are composed largely of nerve fibers. (Fig. I shows the enlargements and the constricted portions. These findings contrast somewhat with the observations of BALFOUR on elasmobranchs, where he finds that the ganglia arise entirely independent of each other, the commissures appearing later as outgrowths from the ganglia.

(4) The rami communicantes arise in the toad in the same manner as in elasmobranchs (BALFOUR). The cord (the gang. lion in elasmobranchs) lies in contact with the nerve from the very first (Fig. 4, Sy.). Later it gradually is removed from the nerve, retaining, however, fibrous connections, which constitute the ramus.

The rami appear earliest in the mid-trunk region, my preparations showing the first one in connection with the

sixth nerve (12 mm. stage). The first and the ninth are the last nerves to develop rami.


For publications prior to 1878, see ONODI, Arch. f. Anat. u. Entwickelungsch. '85, and PATERSON, Philosophical Transactions, '91. Balfour, F. M. '78. Monograph on the Development of Elasmobranch Fishes. Pp. 172

173 and 239-244. 81. Comparative Embryology. Vol. 2, pp. 358-386 and 548. Hertwig, Oscar.

'92. Text-book of Embryology. P. 462. His, W., Jr. '97. Ueber die Entwickelung Bauchsympatheticus beim Hühnchen und

Menschen. Arch. Anat. und Physiol. Anatom. Abteilung, pp. 137

171. (Supplement.) Hoffmann, C. K. '99. Die Entwickelungsgeschichte des Sympathicus bei den Selachiern

(Acanthias vulgaris). Verhand. Akad. IVetensch. Amsterdam.

Tweede Sectie, Deel 7, No. 4. '02. Die Entwickelungsgeschichte des Sympathicus bei den Urodelen.

Verhand. Akad. Wetensch. Amsterdam. Tweede Sectie, Deel 8,

No. 3.

Huber, Carl G. '97. Lectures on the Sympathetic Nervous System. Jour. Comp. Neur.

ol., Vol. 7, pp. 73-145. Marshall, A. M.

'93. Vertebrate Embryology. Pp. 134, 274, 386-387, and 538. McMurrich, J. P.

'03. The Development of the Human Body. Pp. 441-452. Minot, C. S.

'92. Human Embryology. Pp. 630-632 and 485-489.
'03. Laboratory Text-Book of Embryology. Pp. 194-195, 324, 242-

244, and 267-268. Onodi.

85. Arch. f. Anat. u. Entwickelungsgesch.
'86. Ueber die Entwickelung des sympathischen Nervensystems. Arch.

f. Mik. Anat., Vol. 26, Erster Theil, pp. 553-591. Paterson, A. M.

91. Philosophical Transactions, Vol. 181, pp. 159-186.

'03. In Text-Book of Anatomy, edited by D. J. Cunningham. Pp. 673-674. Schenk and Birdsell. *79. Ueber die Lehre von der Entwickelung der Ganglien des Sympa.

theticus. Mittheil. aus d. embryolog. Instit. Wien.



Even a superficial and casual examination suffices to convince one that the commonly recognized varieties of activityreflex, instinctive, voluntary, habitual. etc.,—are intergrading types, not sharply separated classes. Concerning the fact of the existence of clearly definable types of action there is no dispute; concerning their genetic relations there is surprising lack of agreement. Some maintain, with SPENCER, that activity developes from the simple to the complex, from reflex action, through instinctive, to voluntary action. Others, especially those who have attended more carefully to the development of action in the human subject than in the animal kingdom generally, with equal assurance insist that the true and primary course of development is from the relatively complex, variable, and apparently voluntary act to the reflex, automatic and habitual. It is my purpose in this discussion of the subject to try to show that these two courses of development are supplementary rather than contradictory, that phylogeny presents us with facts which favor the former view, ontogeny with facts which favor the latter.

For present purposes it will suffice if we select as essentially important types of action the reflex, the instinctive, and the voluntary. An examination of typical acts to which we should unhesitatingly apply these terms indicates that the types may be defined in terms of the complexity and variableness of action. The reflex act is simple and uniform; the instinctive act is more complex as well as more variable; the voluntary act is either simple or complex and extremely variable—unique. These facts are conveniently expressed in the following simple classification :

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