PR GRESSION . I ND RETR GRESSI ON. 



l8l 



Eolis has no liver. With so much stomach it can carry on the 

 process of digestion -without the aid of that organ, so troublesome to 

 man and beast. A row of hei)atic cells extending part way along the 

 intestine represents the rudiment of a liver, or its vestige. 



Where ai-e the lungs ? Nowhere or, rather, everywhere. No 

 part is specialized and set apart for aerating the blood. In the vital 

 economy of this sea-slug, there is but little division of labor. The 

 surface is soft tissue, covered with vibrating cilia, and currents of wa- 

 ter, set in motion by the cilia, How around the tissue and yield oxygen 

 to its blood. 



Perhaps the gelatinous knob you detached was not an Eolis, If 

 your knife reaches a stomach which is not arborescent, you may have 

 a Doris. The dorsal papilhie of Doris are genuine lungs, but they 

 breathe for only part of the body. They aerate only the blood which 

 goes to the liver, an organ which appears now, not as a row of bile- 

 cells, but as a well-defined gland. The foot shares the labor of the 

 lungs, they breathing for the liver, it for the rest of the body. 



FUi. 1. DOIUS LACINA. 



In Eolis the quill-like diverticula of the stomach are placed in rows; 

 in Doris the leaf-like, moss-like, or flower-like branchiae are gathered 

 into clusters (Fig, 1). Our first woodcut represents a Doris {Doris 

 lacina), with two horn-like antenna^ on the head ; and on the back, at 

 the other extremity, a tuft of crimson leaves finely reticulated and 

 deeply lobed. The second cut represents a Doris (Doris plumMlata), 

 with frond-like antemiiB and a luntj resemblins; tufts of delicate sea- 

 weed wrought into an eight-rayed star. Another Doris wears its lung 

 like a brilliant flower, another like a begemmed tiara, Doris can 

 draw his lungs into his body or throw them out at pleasure (Fig. 2), 



Dendronotus may be known, as its name implies, by its branching, 

 tree-like gills. If we leave the rocks and wharf-posts, and examine the 

 laminaria (oar-weed), or ulva (sea-lettuce), we may find another mem- 

 ber of this family. Aplysia is known to fishermen under the name 

 of "sea-hare." A hump on its back calls up the image of a camel 

 rather than that of a hare. If you make a dissection you will find 

 that an idea has been borrowed from the camel's stomach as well as 



