26 TUNICATA. 



is, within the vessels,"^ which by their reticulation 

 make the spaces — the blood-globules wind along, 

 moving by jerks as impelled by the pulsations of 

 a heart set in a distinct cavity below the lower 

 extremity of the breathing sac. This blood-circu- 

 lation is intermittent in duration, and reversible in 

 its course. For instance, in Perophora, after about 

 a hundred regular pulsations, during which the 

 blood-globules have been uniformly driven from 

 left to rights suddenly the heart ceases to beat, the 

 globules rest in their course, and all is still. In 

 a few seconds the pulsations begin again, and pro- 

 ceed with as much regularity as before ; but the 

 course of the circulation is reversed, — it is now from 

 right to left. 



The stomach in this Class is a dilatation or 

 chamber of the alimentary canal, the surface of 

 which is surrounded by a glandular mass, perform- 

 ing the functions of a liver : the bile secreted by 

 the latter finds its way into the stomach through 

 perforations in its walls. The intestine does not 

 reach to the exterior of the animal, but terminates 

 loosely in a cavity which opens by the secondary 

 orifice. Not only the remains of the digested food, 

 but also the eggs, find their way out through this 

 aperture. I have seen the globular crimson eggs 

 of the little Cynthia grossularia shot out from this 

 orifice to the number of a dozen or more in suc- 

 cession, and with a propellent force that carried 

 them up perpendicularly to a height equal to ten 

 times that of the animal. 



So far as is known, the sexes are united in the 

 same individual. 



* Rather grooves, or open canals, and not true tubular 



vessels. 



