OP ARTS AND SCIENCES. 99 



the intestine these cells are arranged in longitudinal bands, as if they 

 covered the intestinal network of blood-vessels. They contain numer- 

 ous golden-brown drops. In the posterior part of the intestine these 

 drops are still present in the liver cells, but they are colorless. Over 

 the anterior part of the intestine a few of these brown drops are to be 

 found, which are much larger than those met with over the rest of 

 the alimentary canal. They are here seen to have a distinct limiting 

 envelope, which is frequently broken, so that the contents of the drop 

 have escaped. In such cases it appears to be the envelope that gives 

 color to the drop. No such marked distinction of parts is visible in 

 the drops occupying the cells upon the rest of the intestine. Over 

 the whole of the cesophagus, however, the drops are larger than else- 

 where, and most of them show a limiting membrane; this is especially 

 noticeable in the anterior part of the oesophagus. The transition in 

 the size of the drops is gradual, and does not sharply mark off the 

 oesophagus from the intestine. 



Floating in the body cavity are found globular cells, which contain 

 very numerous brown drops that are frequently large, and have a 

 limiting membrane. These cells often become compacted together 

 into large masses. Clear, globular " lymp-cells " are also found float- 

 ing in the body cavity. 



Tlie Vascular System. 



The vascular system consists of a dorsal and a ventral vessel, 

 united by a plexus in the head and one in the region of the pavilion, 

 and by numerous vessels surrounding the alimentary canal. The dor- 

 sal vessel is covered, except in the pharyngeal and part of the oesopha- 

 geal region, by the liver cells, and is contractile, whereas the 

 ventral vessel is free from liver cells, and is not contractile. In the 

 eiglith, ninth, and tenth segments these two vessels are united by lat- 

 eral branches, which float freely in the body cavity, one on each side 

 ill each segment. Like the dorsal vessel, they are contractile. There 

 are often found traces of a vascular network lying beneath the liver- 

 cells of the intestine and also uniting the dorsal and ventral vessels ; 

 but owing to its being hidden by the liver-cells, I have been unable to 

 trace it out satisfactorily. 



The plexus uniting the two vessels in the head has been figured 

 and minutely described by Perrier ('72, p. 79) for Dero ohtusa. In 

 mounted specimens the blood-vessels are rarely to be seen, and are 

 never visible throu<rhout their entire course, while in the liviiiij animal 

 their observation is difiicult, because they are invisible except when 



