694 CLASS xi. 



The nervous system presents a single ganglion, which in the 

 Ascidice is placed on the internal covering of the body, usually 

 regarded as the mantle, between the two tubes into which the body 

 is elongated. Besides other nerves which radiate from this ganglion, 

 there appears to arise from it a nervous ring that surrounds the 

 tube by which the water penetrates (the oral and respiratory tube). 

 Other ganglia which are noticed in Ascidians by some writers, are at 

 the least to be regarded as doubtful 1 . In Salpa a ganglion (or a 

 nerve-mass formed of several ganglia united) lies close behind the 

 anterior, broader opening on that surface of the body which is directed 

 upwards 2 . Several nerves run radiately from this nerve-mass. 



Vestiges of organs of sense are not entirely absent. In the 

 Ascidice at the branchial aperture a circlet of small filiform feelers, 

 sometimes digitally incised or pennated, is found. In the Salpce 

 there lies in front of the central mass of the nervous system an 

 organ of an elongated form, consisting of two laminae with an 

 internal margin smooth and an external striated, which ESCHRICHT 

 regards as an organ of feeling and compares with the four lamellae 

 which surround the mouth in bivalve molluscs 3 . Organs of sight 

 also have been observed in the Ascidice. There are found both 

 around the branchial aperture of the mantle and around the aper- 

 ture towards which the extremity of the intestinal canal proceeds, 

 a ring of eye-points, often of a yellow colour 4 . [In Salpce a vesicle 



1 Thus SCHALK, whose Dissert, de Ascidiarum Structure*, I am acquainted with 

 from citations alone, records a nerve-ganglion in the posterior part of the body, 

 between the convolutions of the intestine ; GRANT speaks even of three ganglia, Out- 

 lines of Comp. Anat. 1811, pp. 205, 206. Compare on the nervous system of the 

 Ascidice, CUVIER Sur les Ascidics, p. 15, PI. n. fig. 2, c, fig. 5, g. SAVIGNY Mem,. 2, 

 pp. 117, 1 1 8, PI. x. fig. 2, i D, &c. 



2 This position of the central portion of the nervous system caused ESCHRICHT to 

 give to the surface the name of ventral side. See on the nervous system of Salpa 

 MEYEN 1. 1. s. 395, and the fig., ESCHRICHT Anat. physiol. Undersogelse over Salpeme. 

 Kjobenhavn, 1840, 4to, printed from the Vidensk. Selsk. Naturvid. og math. STcr. VIII. 

 pp. 1214, Tab. i, fig. 3%, Tab. u. fig. 8u, fig. 12 ; MILNE EDWARDS in CUVIER R. 

 Ani., ed. ill., Mollusq. PL 120, fig. i b, a, PI. 121, fig. 2 a, li, fig. 2 6. 



3 [HUXLEY Anat. of Salpa and Pyrosoma, Ph. Trans. 1851, p. 571, calls this 

 " lanf/liches organ" of ESCHRICHT " lanyuet." He supposes that it may subserve the 

 gustatory function. It floats freely in the respiratory cavity to which it is attached by 

 its base.] 



4 GRANT Outlines, p. 361, says that in Ascidia (Phallus ia) intestinalis eight red 

 eye-points lie round the branchial opening, and six around the efferent tube ; so also, 

 according to the investigations of WILL in various species of Cynthia SAV. and Clave- 



