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
Catalogue details

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.

    166/482 (page 162)
    i enveloped with a layer of black pigment.® Each of these bodies receives a nervous filament from the cerebral ganglion. Undoubtedly, these fila- ments are optic nerves, and the cylindrical bodies are light-refracting and 1 ight-con cent rat ing organs.(6> Many of the Dorsibranchiati are entirely without eyes, having only the eye-specks; but others, belonging to the Amphinomae, Nereideae, Euniceae, and Aphroditae, have two to four very distinct eyes.® In these, there is an eye-ball invested with a black or brown pigment layer: and this layer often has, above, a very distinct round pupillary opening, covered by the skin, which bulges out like a cornea. At the central portion of this layer, there is concealed a transparent body, which is very probably sur- rounded by a retina-like expansion of the optic nerve. The optic nerves which are given off usually from the upper surface of the brain have, after a short course, and before entering the pigment layer of the eye, an enlarge- ment. It is said that with some the light-refracting body and the pupillary opening are wanting. In such cases, the eyes could only distinguish light from darkness.® III. Organs of Hearing. § 161. Although it has never been doubted that the Annelides can perceive sounds, yet it is of late only that the attention has been directed to the locality of the auditory organs. The two vesicles, which, with some Chae- topodes, are situated near the oesophageal ring, and contain crystalline bodies, may be regarded as simple Vestibula, containing many otolites.(1) 5 Weber was the first to show that the black specks of Sanguisuga officinalis were really eyes (Meckel's Arch. 1827, p. 301, Taf. III. fig. 24). This has been confirmed by Brandt (Med. Zool. i. p. 251, Taf. XXIX. A. fig. 10-12), and more re- cently, Wagner has discovered in the interior of the pigment layer, a transparent body, composed, he thinks, of two parts, a crystalline lens and a vit- reous portion ; see Wagner, Lehrbuch, d. ver- gleicli. Anat. 1835, p. 428 ; also Lehrb. d. speziellen Phys. 1843, p. 383, and, Icon, physiol. 1839, Tab. XXVIII. fig. 16. 6 Brandt has been able to trace the ten optic nerves of Sanguisuga officinalis from the brain even to the eyes (Med. Zool. loc. cit. p. 250, Taf. XXIX. B. fig. 2).* 7 With Glycera, Aricia, Arenicola, and Cir- ratulus, the eyes are wanting. With Goniada, and Nephtys, there are only simple pigment specks upon the head. With Eunice, Phyllodoce, and Alciopa. there are two eyes ; and four with Nereis, Syllis, Hesione, and Amphinome. The genus Al- ciopa is well suited, from its large size, for the dissec- tion of these organs. & For a most detailed description of the eyes of Nereis, we arc indebted to Muller (Ann. d. Sc. Nat. XXII.. 1831, p. 22, PI. IV. fig. 6 10), and Wag- * [ § 150, note 6.] For further details on the ocu- lar organs of the Hirudinei, see Moquin-Tandon, loc. cit. Ed. 1846, p. 80, PI. VIII. fig. 11. Accord- ing to him, they contain neither a lens nor a vitre- ous humor, and are only light-perceiving organs. Bee also Ley dig (loc. cit. p. 129) who makes the following statement upon the nature of these bodies ner (Lehrb. d. Physiol, p. 383, and Icon, physiol. Tab. XXVIII, fig. 15). Wagner, who, formerly (Zur vergleich. Physiol, d. Blutes, 1833, p. 55), could not, any more than Muller, perceive the light-refracting body, has at last seen it distinctly. For my own part, I can confirm its presence in the two eyes of Eunice gigantea, which have a circu- lar pupil. According to RathkC (De Bopyro et Nere'ide, p. 44, Tab. II. fig. 4, 5) the eyes of Ne- reis pu/satoria and lobu/ata want the pupil, although it is present with those of Nereis Dumer- ilii. According to Wagner, the pupil is wanting with the two posterior eyes, but is present with the two anterior ones, with most of the Nereideae. 1 I have compared the swellings noticed upon the oesophageal ring of Arenicola, by Grube and Stan- nius (see Wiegmann's Arch. 1841, I. 166), to the auditory vesicles of Mollusks, and their contents to otolites *, since then, Quatrefages has recognized the presence of similar auditory organs containing many otolites with two species allied to Amphicora (Compt. rend. XIX. 1844, p. 195, and Ann. d. sc. Nat. 1844, II. p. 94). Frey and Leuckart (Beitr. &c. p. 81), after a very careful examination of the organs of Arenicola, which I have regarded as au- ditive, have confirmed this opinion. with Piscicola: “They receive no nerve, neither do they contain a light-refracting body. I regard them as simple ornaments, wholly analogous to the corresponding pigment dots on the pedal shield, with which they also correspond in color and dis- tribution.”— Ed.