106 A. OKA. 



median tentacle on the anal tside, making the total num1)er «xld. 



There can be uo d(juLt that the function of the tentacle« is three- 

 fold, äer\ing for respiration, for collecting food and for feeling. 

 Of these, however, the first seems to l)e their principal office, 

 when we consider the large extent of their surface exposed to 

 water, and the constant current kept np in the latter hy a special 

 contrivance, as well as the perigastric fluid that circulates within 

 their lumen. The Tentacles thus bear a close resemblance to the 

 fringed arms of ßrachiopods. 



Circulation. The perigastric fluid contained in the general body- 

 cavitv may justly be regarded as representing the blood. Of its 

 nature and the mechanism of circulation, little was known before. 

 There are no special orgarjs, such as heart and blood vessels, and the 

 only means of driving the perigastric fluid is the supposed ciliation 

 on the lining epithelium of the general body-cavity. The nutritive 

 part of the food taken up by the alimentary canal is conveyed to all 

 parts of the body by this fluid. It is transparent, colorless, and has 

 no taste. Water seems to constitute the greater part of its con- 

 stituents. 



The fluid contains, floating in it, numerous round cells, each 

 with a large vacuole almost filling up its body and filled with a 

 refi-actile fluid (fig. 20, PI. XYIII). The nucleus is pushed against 

 the wall by the vacuole. The study of the development of polypides 

 in the statoblast shows that these free cells are derived directly from 

 the iiianular mass that constitutes the main contents of the statoblast, 

 and in young stages they contain similar granules instead of the 

 vacuole. It is therefore plain that they are, at any rate, nutriment 

 carrying cells, which might be regarded as blood corpuscles. 



