148 HYATT, 



the weakness of the valve, which gives way before unusual 

 pressure. 



The eliminated nutriment transudes through the mem- 

 branes of the stomach and intestine into the perigastric 

 chamber, and there mingling with the circulating medium 

 is conveyed by it to all parts of the body. 



The residuum of the digested food is admitted grad- 

 ually to the intestine through the intestinal valve, and as- 

 suming a more solid appearance, it is slowly discharged 

 from the anus by the agency of the transverse parietal 

 muscles. 



These excrements are oval, and compounded of brown- 

 ish colored refuse cemented by transparent gelatinous mat- 

 ter. They correspond in shape with the intestine, and have 

 diiferent forms according to the genus of the species, from 

 which they are thrown off, being very much elongated in 

 Fredericella, broader in proportion to the length in Pluma- 

 tella, and very broad in Pectinatella, thus agreeing exactly 

 with the gradual increase in the transverse diameter of the 

 intestine from Fredericella to Pectinatella. In Cristatella 

 they were not closely observed, but probably are more or 

 less flattened in correspondence with the very flat intestine 



of that genus . 



CIRCULATION. 



The interior of the polypide and ccemBcium is filled 

 with a colorless fluid which is kept in circulation by the 

 cilia on the epithelial membrane. They cover the entire 

 surface of the endocyst, including the ceiling of the lopho- 

 phore ; but, as previously observed by Professor All- 

 man, do not occur upon the alimentary canal. There are 

 two principal currents maintained in each polypide by 

 these cilia, one passes posteriorly along the dorsal side, 

 enters the arms, and, being deflected upon itself at their 

 extremities, courses along the ceiling of the lophophore, 

 and returns to the ccenoecium along the ventral side. 

 These currents can be readily observed by the aid of 

 the numerous organisms, many of them probably para- 

 sitic, which float in the fluid, sometimes in such num- 

 bers as to interfere with the examination of the inter- 



