116 TUNICATA. ASCIDIAIUA. 



The body is besides composed of muscular fibres, and distinct 

 blood-vessels ; the alimentary tube is open at both ends ; and 

 a mass of gemmae or ova, either solitary or together in a common 

 envelope, seems to form the ovaries. The respiratory organ in 

 this class is always interior, formed of two membranous reticu- 

 lar leaflets, sometimes constituting a sort of sac, sometimes 

 forming two bands of unequal length, united by one end. None 

 of these animals possess retractile tubes for locomotion. Their 

 body, soft or coriaceous, is generally fixed, either by itself or in 

 connection with others of the species, to foreign substances. No 

 trace of sexual organs have been discovered. 



Many of the animals of this class, from their union in a com- 

 mon mass, seem at first sight to form compound animals like 

 the polypi ; but this wide distinction is to be remarked between 

 them and the lower families in the zoological scale, that the 

 aggregated Tunicata are independent and individual beings, 

 each being provided with a mouth and aperture for digestion, 

 applicable to their individual wants, and unconnected with the 

 general nutrition of the common mass. 



Lamarck divides this class into two orders : 

 Order I. ASCIDIARIA. Animals disunited, either isolated, or 

 in groups without internal communication, and not forming 

 essentially a common mass. 



Order II. BOTRYLLARIA. Agglomerated animals, always unit- 

 ed, and constituting a mass with a common covering. 



ORDER I. ASCIDIARIA. 



Animals disunited, either isolated, or in groups without internal 

 communication, and not forming a common mass. 



The animals of this order have the body enveloped in an external tunic or bag 

 with two openings, one for receiving water for the respiratory apparatus and their 

 aliment, and the other for rejected matters. These animals are fixed to rocks and 

 other bodies, and are deprived of locomotion. Their principal sign of life consists 

 in the absorption and evacuation of water by one of their orifices. 



Gen. 1. MAMMARIA, Lam. 



Body free, naked, oval or subglobular, terminated at the sum- 

 mit by a single opening ; no tentacula at the orifice. 

 M. mammilla, Lam. Body conical, ventricose, white. Inhabits the 



Norwegian seas Lam. iii. 129. 



M. varia, Lam. Body ovate, varied with white and purple. In- 

 habits Northern Ocean. Lam. iii. 130. 



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