TUNICATA. 115 



A. agglulinans, Lam. Sheath variously curved, subclavate, attach- 

 ing to other bodies ; disc of the club with distinct tubular spines, 

 the rest of the tube covered with fragments of sand, shells, and 

 madrepores. 3 inches long. Inhabits seas of New Holland 

 Lam. v. 430. 



CLASS III. TUNICATA. 



Gelatinous or coriaceous biforous, bitunicated animals, isolated, 

 in groups, or often joined together in a common mass. 



THE place which the animals of this class ought to occupy in 

 an arrangement corresponding to their organization has not 

 been satisfactorily ascertained. Cuvier places them among his 

 Molluscous animals, in the class Acephala, and makes them the 

 second order of this class, under the title of Acephalous Ani- 

 mals without shells ; while Lamarck arranges them between the 

 Echinodermataand worms. Latreille places them after the Ento- 

 %oa, and they form the fourth order of Blainville's class Ace- 

 phalophora, under the name of Heterobranchiata. In point 

 of fact, there seems to be, both among the vertebral and inverte- 

 bral animals, more than one series of forms and structure, which, 

 either in the descending or ascending scale, where the most 

 nearly allied groups in point of structure are arranged in se- 

 quence, will always interfere to disturb any continuous or su- 

 bordinate arrangement. The existence of these parallel groups 

 presents formidable difficulties to the classification of animals in 

 one unbroken series ; but the establishment of closely connect- 

 ed groups into natural families, a plan which has been largely 

 adopted by the recent writers on the classification of animals, 

 renders the arbitrary limitations of systematic writers of objects 

 in themselves unlimited a matter of less consequence. We have 

 therefore followed M. Cuvier in placing the class Tunicata un- 

 der the general head Mollusca. 



The animals of the class Tunicata have an oblong irregular 

 body, and as if divided interiorly into many cavities. They have 

 no head ; possess no distinct organs of sensation ; and no sym- 

 metrical or similar parts in pairs. Some tubercles and threads 

 discovered in their body are presumed to form the nervous system. 



