162 THE ANNELIDES. "^ 151. 



enveloped wi'th 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 

 light-concentrating organs/'"' 



Many of the Dorsibranchiati are entirely without eyes, having only the 

 eye-specks ; but others, belonging to the Amphiuomae, Nerei'deae, 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 oif 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. 



§ 151. 



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 VestiOula, containing many otolites.'" 



5 IVeber vias the first to show that the black ner (Lehrb. d. Physiol, p. 383, and Icon, physiol. 



ep^cks of Sanzuisui^a officinalis were really eyes Tab. XXVIII, fig. 15). IVag-ner, v/ho, formerly 



{Meckel's Arch. 1827, p. 301, Taf. III. fig. 24). (Zur vergleich. Physiol, d. Blutcs, 1833, p. 55), 



This has been confirmed by Brandt (Med. Zool. I. could not, any more than Muller, perceive the 



p. 251, Taf. XXIX. A. fig. 10-12), and more re- light-refracting body, has at last seen it distinctly, 



cently, fVa^ner has discovered in the interior of For my own part, I can confirm its jireseuce in the 



the pigment layer, a transparent body, composed, two eyes of Eunice ^is^antea., which have a circu- 



he thinks, of two parts, a crystaUine lens and a vit- lar pupil. According to Rathkt (De Bopyro et 



reous portion ; see fVa^ner, Lehrbuch, d. ver- Nereide, p. 44, Tab. II. fig. 4, 5) the eyes of Ne- 



gleich. Anat. 1835, p. 428 ; also Lehrb. d. speziellen rets pnlsatoria and lohulata want the pupil, 



Phys. 1843, p. 383, and. Icon, physiol. 1839, Tab. although it is present witii those of iVflreis £)u7«er- 



XXVIII. fig. 16. ilii. According to Warner, the pupil is wanting 

 •) Brandt has been able to trace the ten optic with the two posterior eyes, but is present with the 



nerves of Sang-uisuga officinalis from the brain two anterior ones, with most of the Nereideae. 



even to the eyes (Med. Zool. loc. cit. p. 250, Taf. 1 I have comi)ared the swellings noticed upon the 



XXIX. B. fig. 2).* oesophageal ring of Arenicola, l>y Grube and Stan- 

 7 With Glycera, Aricia, Arenicola, a.m\ Cir- nius (see IViesTnannKt Arch. ISil, I. 166), to the 



ratnliis, the eyes are wanting. With Goniada, auditory vesicles of MoUusks, and their contents to 



and iVe;yA i;/s, there are only simple pigment specks otolites; since then, Quatrejages has recognized 



upon the head. With Eunice, Phytlodoce, and the presence of similar auditory organs containing 



Alciopa. there are two eyes ; and four with Nereis, many otolites with two species allied to Amphicora 



Si/llis, Hesione, a.ml Amphinome. The genus ^/- (Compt. rend. XIX. 1844, p. 195, and Ann. d. so. 



ciopa is well suited, from its large size, for the dissec- Nat. 1844, II. p. 94). Frey and Leuckart (Beitr. 



tion of these organs. &c. p. 81), after a very careful examination of the 



^ For a most detailed description of the eyes of organs of Arenicola, which I have regarded as au- 



Hereis. we are indebted to Muller (Ann. d. Sc. ditive, have confirmed this opinion. 

 Nat. XXII. 1831, p. 22, PI. IV. fig. 6 10), and fVag- 



* [ § 150, note 6.] For further details on the ecu- with Piscicola : "They receive no nerve, neither 



lar organs of the Ilirudinei, see Moquin-Tandon, do they contain a light-refracting body. I regard 



loc. cit. Ed. 1846, p. 80, PI. VIII. fig. 11. Accord- them as simple ornaments, wholly analogous to the 



Ing to him, they contain neither a lens nor a vitre- corresponding pigment dots on the pedal shield, 



ous humor, and are only light-perceiving organs, with which they also correspond in color and dis- 



Bee a\so Leydif; (loc. cit. p. 129) who makes the tribution." — Ed. 

 following statement upon the nature of Uiese bodies 



