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SHELL GALLERY. 



animal, which lives on a muddy bottom, in from five to twenty fathoms, 

 resembles a conical sac fixed by the broader end, of grayish green 

 colour and about 4 inches in height. At the narrower end are two 

 orifices, one terminal — the branchial orifice or mouth, and the other 

 a little lower — the atrial orifice : the former has eight lobes and the 

 latter six. 



When the Ascidian is undistubed, the orifices are wide open, and 

 currents enter by the branchial and leave by the atrial orifice. On 

 the least alarm, the orifices close, jets of water being at the same 

 time squirted out ; hence the popular name " Sea-squirts " given to 

 these animals. 



The Ascidian is orientated as follows : hold the animal with the 

 branchial orifice pointing forwards and the atrial upwards ; the 

 branchial orifice will be anterior and the opposite end posterior ; the 



Fig. 2. 



Diagrammatic section of Ascidia representing the three sacs, and the branchial 



sac as the pharjmx or throat, 

 a, branchial ; and 6, atrial orifice; c, tunic or test; d, mantle; e, branchial sac; 



/, gullet; g, stomach ; h, anal orifice; i, dorsal lamina; dotted line indicates 



the endostyle. 



atrial orifice will lie on the upper or dorsal aspect, the opposite 

 aspect being lower or ventral, and the sides right and left. The 

 aspects, in fact correspond with those of a vertebrate animal. A 



