ANATOMY AND PHYSIOLOGY. 2-) 



communication with each other, though they lie in contact and 

 are cemented together ; nor are they connected with any duct, 

 or in any way open into the alimentary tube. Blood-channels 

 are hollowed out, as it were, amidst the vesicles; and the 

 reproductive organs ramify throughout the agglomerated mass 

 which overlies, for the most part, the true hepatic organ. 

 These vesicles will therefore act as a sort of packing to the 

 parts of these organs, and will give support and protection to 

 them, whatever higher function they may have to perform. 

 They may likewise assist the heart in the performance of its 

 work by their resiliency when the mass is gorged with blood ; 

 for it is evident that, when the interstices or blood-channels 



FIG. 3. Hepatic taibes in Ascidia affinis. The branches terminate in blind 

 sacs, and are rounded and enlarged a little. Highly magnified (1 in. 

 object-glass). 



are filled, the vesicles will be more or less collapsed in pro- 

 portion to the pressure of the blood-current ; and when the 

 latter changes its direction the reaction will be assisted by 

 their expansion. In our present state of knowledge, however, 

 nothing positive can be said of the uses of this very curious 

 structure. 



The true hepatic organ, as already intimated, lies beneath 

 this vesicular mass, and forms a thin coating on the surface 

 of the intestine. In all the examples observed it is composed 

 of delicate tubes, which divide dichotomously, but frequently 

 without much regularity. At the points where the branches 

 are given off, the tubes are usually enlarged, and the twigs 

 terminate in rounded extremities more or less inflated (fig. 3). 



