Comparative anatomy / by C.Th. v. Siebold and H. Stannius ; translated from the German, and edited with notes and additions recording the recent progress of the science by Waldo I. Burnett.

  • Karl Theodor Ernst von Siebold
Date:
1854
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Licence: Public Domain Mark

Credit: Comparative anatomy / by C.Th. v. Siebold and H. Stannius ; translated from the German, and edited with notes and additions recording the recent progress of the science by Waldo I. Burnett. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    which are nearly blended together into one, and whose closely-successive ganglia correspond numerically with the segments of the body.® 4. With those Chaetopodes which have external branchiae, the nervous system is most highly developed, but has wide variations as to its whole or its details, according to the more or less complicated structure' of the cephalic extremity and segments of the body. With those species which are without antennae and eyes, the ventral medulla is composed of two contiguous cords the enlargements of which are indistinct and not sharply defined.<B) These two cords are separated at the cephalic extremity, and terminate either, by a ganglion on each side without apparently forming by a commis- sure an cesophageal ring,<7) or by encompassing the oesophagus, and forming a ring through a ganglion lying upon it.(8) With some, the two parallel cords- are without ganglia but are reunited at each segment of the body by two transverse threads.® With others, this connection occurs through transverse threads and ganglia.(10) There are many Branchiati with which the two cords are so closely contiguous that they are separated only by a longitudinal furrow. Their round or elongated ganglia are then common, and succeed each other at longer or shorter intervals.™ With an entire series of the Dorsibranchiati, the ventral ganglia are so closely approximated that the interganglionic cords appear wholly wanting.™ The brain is composed of only two ganglia, which are more or less blended into one with the Gapitibranchiati, and with those Dorsibranchiati whose head is very slightly developed; u3) while with the other Dorsibranchiati whose head is distinct and the eyes and tentacles very much developed, it is the product of the fusion of many ganglia.<14) 5 See Gruithuisen, in the Nov. Act. Acad. XIV. 1828, p. 412, Tab. XXV. fig. 3-5 (Chaeto- gaster diaplianus)Henle, in Muller's Arch. 1837, p. 85, Taf. VI. fig. 2, 3, 8, x, y (Enchi- traeus); Roth, De Animalium invertebratorum systemate nervoso. Wirceburg, 1825, fig. 3 ; and Morren, loc. cit. p. 117, Tab. XIX.—XXIII. (Lumbricus terrestris). In the common Lum bricus, two pairs of nerves (Nervi annulares) pass off laterally from the cen- tre of the ganglionic enlargements ; and between every two ganglia, exceptionally, there passes off another pair (Nervi inter annulares) which are distributed to the transverse muscular septa ; see Morren loc. cit. The nervous system of Sternas- pis thalassemoides i3 quite different, and appears retrograded to the type of that of the Sipunculidae, for the ventral medulla consists only of a simple cord which is enlarged at the caudal extremity j see Will, in Muller's Arch. 1842, p. 427. 6 Arenicola, Ammotrypane, and Terebella. 7 Arenicola; see Grube, Zur. Anat. d. Kiemen- wiirmer, p. 17, Tab. I. fig. 7 and Stannius, in Muller's Arch. 1840, p. 379, Taf. XI. fig. 15. 8 Ammotrypane ; see Rathki, in the Nov. Act. Acad. XX. p. 197, Tab. X. fig. 14, 19. 9 Sabella; see Wagner, Isis, 1832, p. 657, Taf. X. fig. 14 5 and Grube, Zur. Anat. d. Kiemenwur- mer, p. 30, Taf. II. fig. 16. 10 Phyllodoce. Here, the transverse threads commence only at the border of the 7ll» or 9lh gan- glion. They alternate regularly with these and disappear towards the last segments of the body ; see Quatrefages, Ann. d. Sc. Nat. II. 1844, p. 95, PI. If. fig. 2, 3. 11 Siphonostomum, Amphitrite, Amphinome, Aricinella, Polynoa, and Aphrodite. With Si- phonostomum, the ventral ganglia are very long ; see Rat like, Danzig. Schrift. loc. cit. p. 90, Taf. VI. fig. 3. Here, the peripheric nerves are given off from the interganglionic cords and not from the ganglia themselves. With Amphitrite, the ventral ganglia are long also, but from the fifth segment of the body they alternate with others that are round, so that each segment has two ganglia. Both of these ganglia furnish exclusively the peripheric nerves, but in front where the round ganglia are wanting, they are furnished also by the interganglionic cords ; see Rathkif, loc. cit. p. 75, Taf. V. fig. 7, 15. With Aricinella (Quatrefages, loc. cit. p. 96, PI. II. fig. 5), and Amphinome (Treviranus, Beobacht. aus d. Zoot. u. Physiol. 1839, p. 83, Taf. XI. fig. 72), the ganglia are very closely set together. With Aphrodite, and Polynoe, the number of ventral ganglia exceeds that of the segments of the body ; see Grube, loc. cit. p. 66. 12 Nereis, Eunice, Glyccra ; see Wagner, in Isis, 1834, p. 133, Taf. I. fig. 11; Muller, in the Ann. d. Sc. Nat. XXII. 1831, p. 22, PI. IV. fig. 10 *, Rathki, De Bopyro et Nereide p. 41, Tab. II. fig. 13 Grube, Zur. Anat. d. Kiemenwfirmer, p. 43, Taf. II. fig. 9 ; and Quatrefages, Ann. d. Sc. Nat. loc. cit. PI. I. fig. 1, 2, 3. 13 Amphitrite, Siphonostomum (Rathki, Dan- zig. Schrift. loc. cit. Taf. V. fig. 7, 14, Taf. VI. fig. 3), and Glycera (Quatrefages, Aim. d. Sc. Nat. loc. cit. p. 96, PI. I. fig. 3)/ H Nereis, Eunice, and Phyllodoce ; seeilful- ler, Ann. d. Sc. Nat. loc. cit. PI. IV. fig. 10 -, Rathki, De Bopyro et Nereide, p. 43, Tab. II. fig. 4, 5, 13 -, and Quatrefages, loc. cit. p. 81, PI. I. fig. 1, 2, PI. II. fig. 1.' * [§ 148, note 13.] See Quatrefages, Ann. d. Sc. Nat. X. 1848, p. 47 (Hermella), and XII. 1849, p. 300 (Chloraema). — Ed.