ox DEA'i:rX)PMEXT ETC. OF PIIOrtONIS. ')()0 



represents a transverse section through the middle portion of the 

 trunk where tlie stomach {sl//i.) joins the intestine {int.). There 

 tlie muscles appear as two small striated masses {/'ef.') lying on 

 l)iHh sides of the intestine. As represented in fig. 57 h, which is 

 taken from the portion of the body wall c()Dtaiiung the nephi'idial 

 canal {nepj'.), each of the nuiscles is in its origin traceal)le to the 

 circular muscle layer {cir.vi.) which is sul)dermally interposed het- 

 ween the ectohlast and the peritoneal epithelium. When these 

 two muscles, in their downward course, reach the level of the 

 terminal portion of the intestine, they fuse together into one on 

 the dorsal side of the intestine. I think that the above men- 

 tioned muscles are a kind of retractors serving to contract the 

 trunk of the larval body. I can not help thinking that the 

 " Afterbänderung " of Wagener ('47) is probably simj^ly the post- 

 erior portion of the nuiscles in question in the proximity of the anus. 

 Vascular sydern. It is a well known fact that the closed 

 vascular svstem of Fhoronis offers one of the greatest obstacles to 

 the idea entertained by some naturalists that the animal is of the 

 Polyzoan type. ]\Iany writers are, therefore, much inclined to 

 attrihute the simple body organization of Fhoronis to secondary 

 adaptation, and to erect the animal into a distinct order very closely 

 related to the C'hordata. Putting aside for the present all the- 

 oretical speculations, it is of great importance in ascertaining the 

 phylogenetic relation of the animal to note that one portion of the 

 larval body-cavities is transformed into a blood vessel, ar.d that 

 the simple and rudimentary vascular system of u4ctinotrocha uudei'- 

 goes a wonderful change and suddenly attains the high organi- 

 sation seen in the adult during metamorphosis. 



Krohn ('50) proved that the " Leherzellen " of Wagener 

 nud Gegexbat'r were really blood corpuscles. Hfwvever, he did 



