EXCRETORY ORGAN OF FRESH-WATER POLYZOA. 363 



.•skeleton, there :ire still the m;iin diiferences concerning the nephridia 

 and blood-vessels. While Vhorouis has Avell developed metaneph- 

 ridia that serve at the same time as the passage for tlie exit of 

 genital products, the Ectoproctons Polyzoa have no structure com- 

 parable to it, the excretory funcrion being here carried on chietiy by 

 leucocytes. Fhoronis has a set of closed bhiod-vessels besides the 

 crelom, whereas in the Ectoprocta it is tiie perigastric fluid that 

 circulates through the body. These ditferences are indeed very great, 

 and should certainly be taken into consideration in discussing the 

 genetic affinitv of these animals. After weighiug these and other 

 important structural diiferences against the superficial resemblance 

 which thev present, we come uncoii(litionally to the conclusion 

 that Phoroitis approaches the Sipunculids more than it does the Ecto- 

 proctons Polvzoa. 



