TUNICATES. 695 



attached to the lower surface of the nerve-mass and containing 

 calcareous bodies would seem to represent the auditory capsule and 

 its otolithes l .~\ Such an organ also, but containing a concrement of 

 a more composite form, was discovered by ESCHRICHT, similarly 

 situated in a simple Ascidian Ghelyosoma Macleayanum, and noted 

 as the auditory organ 2 in 1841. 



The muscular system in Ascidice consists of a layer of fibres, 

 which cross each other on the inner covering of the body (the so- 

 called mantle), but run principally in a longitudinal direction. In 

 the Salpcz muscular bands are seen remote from each other, which, 

 like a girdle not entirely closed at one part, surround the internal 

 cavity of the body, the respiratory space. These bands consist of 

 fibres that run parallel to each other in the direction of the bands, 

 and thus form a right angle with the longitudinal axis of the body. 



On the position of these animals in the natural system there 

 can exist no doubt when they are referred to the common type of 

 the molluscs. They must be regarded as the lowest division of 

 these animals, that immediately close in upon the bivalves. The 

 compound Ascidians in propagating by gems remind us of lower 

 animals of the class of the Polyps. More especially still do the 

 Ascidians resemble the Bryozoa (comp. I. pp. 92, 93), but we should 

 prefer to unite these last with the Mollusca, rather than on account 

 of this affinity to separate the Tunicata from the Mollusca. 



Species of this class are met with in all seas. The Salpce are 

 numerous in the Mediterranean and in the ocean, especially between 

 30 and 40 N. and S. Lat., in colder regions and in higher latitudes 

 they are of more rare occurrence although they extend to 50 N. 

 and S. Lat., and were once observed near the Norwegian coast even 



Una. V. BENEDEN in a species of Ascidia named by himAscidia vitrea, found eight eyes 

 at both openings ; Reck. s. 1. Ascid. simples, p. 61, PL iv. fig. 2. In Ascid. ampullotdes 

 V. BEN. such eye-points cannot be seen, but when young and still moving freely the 

 animal has one or two black eye-points ; ibid. p. 40. 



1 [HUXLEY 1. 1. p. 571, PI. XVI. fig. 2.] 



2 ESCHKICHT Anatomisk Beskrivelslce af Chelyosoma Macleayanum of So WEBBY, 

 Kjobenhavn, 1841, quoted by SIEBOLD Vergl. Anat, I. p. 260 (note), who suspects 

 from the figures of DELLE CHIAJE and SAVIGNY that the organ exists very generally in 

 this class. MILNE EDWARDS (see the figures of Salpa referred to above in the illus- 

 trated edition of CUVIER) thinks that it must be regarded as an organ of vision. 

 That MEYEN had observed this organ lying above the central nerve-mass, I collect 

 from his figure, Tab. xxvii. fig. 18. 



