TUNICATA 



913 



posite mass and the anatomy of a single individual are displayed in 

 fig. 690. Its clusters appear almost completely inanimate, exhibiting 

 no very obvious movements when 

 irritated; but if they be placed 

 when fresh in sea-Water a slight 

 pouting of the orifices will soon be 

 perceptible, and a constant and 

 energetic series of currents will be 

 found to enter by one set and to be 

 ejected by the other, indicating that 

 all the machinery of active life is 

 going on within these apathetic 

 bodies. In the family Polydmidce 

 to which this genus belongs the 

 body is elongated, and may be 

 divided into three regions : the thorax 

 (A), which is chiefly occupied by the 

 respiratory sac ; the abdomen (B), 

 which contains the digestive appa- 

 ratus ; and the post-abdomen (C), in 

 which the heart and generative 

 organs are lodged. At the summit 

 of the thorax is seen the oral orifice, 

 c, which leads to the branchial sac e ; 

 this is perforated by an immense 

 number of slits, which allow part of 

 the water to pass into the space 

 between the branchial sac and the 

 muscular mantle. At k is seen the 



FIG. 690. Compound mass of Amaroiiciumproliferum with the anatomy of a 

 single zooid : A, thorax ; B, abdomen ; C, post-abdomen ; c, oral orifice ; 

 e, branchial sac ; /, thoracic blood-vessel ; i, atriopore ; i', projection over- 

 hanging it ; j, nervous ganglion; k, oesophagus; I, stomach surrounded by 

 digestive tubuli ; m, intestine ; n, anus opening into the cloaca formed by 

 the mantle ; o, heart ; o', pericardium ; p, ovarium ; p', egg ready to escape ; 

 q, testis ; r, spermatic canal ; r', termination of this canal in the cloaca. 



cesophagus, which is continuous with the lower part of the pha- 

 ryngeal cavity ; this leads to the stomach, I, which is surrounded 

 by glandular follicles ; and from this passes off the intestine, m, which 

 terminates at n in the vent. A current of water is continually 



3 N 



