^150. 



THE ANNELIDES. 



161 



often very prominent tactile organs, in the form of processes of variable 

 number and shape, which are situated principally though not entirely upon 

 the cephalic extremity of the body. Those upon the head have been 

 named Antennae, and the others Cirri. These last are often very numer- 

 ous upon the first segment of the body. Both are contractile and usually 

 unarticulated, though sometimes having very distinct joints.® The an- 

 tennae receive their nerves directly from the cerebral ganglion,''*^ while 

 those of the cirri of the first segment, are given oiF from the base of the 

 two lateral cords of the oBSophageal ring, and from the first ventral gan- 

 glion. '^^ 



II. Organs of Ytsion. 



§ 150. 



With nearly all the Capitibranchiati,^' and with many Nemertini, and 

 Lumbricini, the eyes are wanting. But, as visual organs, have been re- 

 garded the brown or black dots, which are two in number with many Nais, 

 four with Tetrastemma, but are innumerable and arranged irregularly or 

 in rows upon the neck, with Folystemma and Nemeries. But these are 

 scarcely more than simple pigment dots.^-' 



With the two to ten eye-specks of the Hirudinei,'"' however, the structure 

 is quite dilFerent. Here the eye^^^ is composed of a transparent cylindrical 

 body, a little attenuated and rounded at its inferior extremity, while the oppo- 

 site one causes the skin to bulge out like a cornea. Its remaining portion is- 



3 The antennae of the Annelides have been dis- 

 tinguislied from those of insects by being termed 

 Tentacula ; for they are non-articulated, while 

 those of insects are articulated. But this distinc- 

 tion is not valid, for, with the Branchiati, there are 

 insensible transitions from the non-articulated ten- 

 tacula to the articulated antennae. But another 

 and more essential difference is, that those of the 

 Annelides are contractile, while those of insects are 

 not. These organs are articulated with Eunice, 

 Peripatus, and Syllis. In this last it is true of 

 the cirri also. The modifications and varieties of 

 the antennae and cirri belong, however, to the 

 province of Zoology. 



4 With Nereis, four nerves pass off from the 

 anterior portion of the brain to the four antennae ; 

 the two external as gustatory nerves and which go 

 to the larger antennae, are largely swollen at their 

 extremity ; see Rathki, De Bopyro et Nereide, p. 

 43, Tab. II. fig. 4, 5. 



5 See Rathki, Ibid. Taf. U. fig. 18, d. d. and in 

 the Danzig. Schrift, loc. cit. p. 76, Taf. V. fig. 14, 

 d.d. 



1 A remarkable exception to this occurs with 

 Amphicora Sabella as described by Ehrenberg 

 (Mittheil, aus d. Verhandl. d. Gesellsch. naturf. 

 Fremde zu Berlin, 1836, p. 2). It has, it would 



appear, two eyes not only at the cephalic extremity^ 

 but at the opposite one also.* 



2 Gruilhuisen (Nov. Act. Acad. Nat. Cur. XI. p. 

 242) has described the two eyes of Nais probosci- 

 dea as i)article3 of pigment enveloped by a sensi- 

 tive parenchyma. But this is not based upon ob- 

 servation, and is an hypothesis only, as Müller 

 has very judiciously remarked (Ann. d. Sc. Nat. 

 XXII. 1831, p. 20). The assertion of Quatrefaffex 

 is of m:ji-e weight (Comp. rend. XIX. 1844, p. 195). 

 He affirms that the pigment specks of many Ne- 

 mertini and of a marhie species allied to Ifais, con- 

 tain really light-refracting bodies, and connect 

 with the nervous centre by particular nerves. 

 The last of these Annelides has similar pigment 

 specks also upon each side of the segments of tha 

 body, which receive each a distinct nerve from the 

 ventral marrow. Is not this species identical with 

 the Nai.i picta described by Dujardin (Ann. d. 

 Sc. Nat. 1839, XI. p. 233, PI. VII. fig. 9) .' t 



3 Clepnin e has two, four or six eyes ; Nephelis, 

 eight ; and Haemopis and Sansuisus^a, ten ; 

 while with Branc/iiobdella, they are wanting^ 

 With this family (the Hirudinei), these organs are- 

 always symmeti'ically arranged upon the neck. 



■i At least with Sans^uiiuira officinalis. 



* [ § 150, note 1.] Quatrefa,s:es (Ann. d. Sc. 

 Nat. X. 184S, p. 48, PI. II. fig. 10, y.) describes 

 two colored points situated on the middle of the 

 brain of Hermella, as eyes. They are composed 

 of pigment and rest directly on the nervous sub- 

 Stance. — Ed. 



t [ § 150, note 2.] Quatrefases (Compt. rend. 

 11* 



Dec. 31, 1849) has found very perfect eyes with 

 Torrea vitrea, consisting of a crystalline lens, % 

 choroid coat, a vitreous humor, a transparent cor- 

 nea, &c. He thinks also that he has discovered 

 with Sabella eyes situated on the branchiae ' — 

 Ed. 



