374 



TUNICATA. 



cules : the stomach is capacious, and covered with parallel rows of 

 large white filaments, that seemingly represent the liver ; and 

 the alimentary canal, which is perfectly simple, runs to the pos- 

 terior extremity of the animal, and terminates there by a wide 

 opening.* Two oblong bodies, each consisting of a granular 

 substance, are seen upon the ventral surface of the body lodged 

 between the external and internal membranes, which no doubt 

 are the ovaria, and form a reproductive system as devoid of com- 

 plication as that of the sessile Ascidians. 



(410.) A very remarkable feature in the history of these animals 

 is, that many species are found swimming together in long chains, 

 apparently adhering to each other by little suckers, but without 

 organic connexion ; and, what is still more strange, it would appear, 

 from the observations of M. de Chamisso,'j" that such aggregated 

 animals give birth to insulated individuals of very different ap- 

 pearance, which in their turn reproduce concatenated forms re- 

 sembling their progenitors, so that the alternate generations are 

 quite dissimilar both in conformation and habits. 



The last families of TUNICATA which we have to notice, would 

 seem to constitute a connecting link between the MOLLUSCA 

 and the BRYOZOA, which latter in many points of their anatomy 

 they much resemble. These animals generally are exceedingly 

 minute, and individually present an organization analogous to that 

 of Ascidians. At first it would appear that they are detached 

 from each other, and, like Salpa, are endowed with a power of 

 locomotion ; but subsequently they become aggregated in groups, 

 either incrusting foreign bodies, or else, uniting together to form a 

 mass of definite shape, they seem to enjoy to a certain extent a com- 

 munity of action. They are arranged by Cuvier^: in three princi- 

 pal groups, distinguished by the following characters. In the first 

 (Botryllus), the little bodies of the individual animals are ovoid ; 

 but they fix themselves upon the exterior of sea-weed or other 

 substances in regular bunches, consisting of ten or twelve, arranged 

 like the rays of a star around a common centre. The branchial 

 orifices in such are all placed around the circumference of the star, 

 while the excretory apertures open into a common cavity in the 



* For excellent drawings, representing the anatomy of various Salpae, the reader 

 is referred to the Descriptive and Illustrated Catalogue of the Physiol. Series of Comp. 

 Anat. contained in the Mus. of the Royal Coll. of Surgeons, London, vol. i. plates 

 6 and 7. f Dissert, de Salp&, Berlin, 1830. 



t Regne Animal, vol. iii. p. 168. Bar^t/f, bunch of grapes. 



