ON UEVEL0P3lEXr ETC. OF PIIORONiS. ÖÜO 



close of the larval life the blood system in the followuiy condition : 



1. Blood corpuscles aggregated in two or more masses, I ging 

 in the hody-cavity of the preoral lobe, i. e., in front of the septum. 



2. A blood vessel for /tied on the dorsal 7vall of the sto/i/aeh, 

 a //larked structure of the larva. 



3. The splanchnopjleure, ivhich in the region of the sto/n<ich 

 for//i,s a loo.^e sac surrounding the gut. 



4. Ctecal prolongations of this sac. 



~). Geral prolongations into the rudiz/ients of the adult ten- 

 tacles " ('82"'83, I.e., i>. 377). Besides, the author insists on the free 

 communication betAveen tlie splanchnopleuric sac and the 1)ody- 

 cavity in trout of the septum. Thus it may be understood tliat 

 Caldwell detected only one vessel (dorsal) in Actinotrocha and 

 thought tlie ring vessel of the adult was produced from the 

 splanchnopleuric sac around the stomach. 



Masterman's views ('97) of the vascular system ditier greatly 

 from those of all the others above quoted. The subneural sinus 

 is said to c(jmniiuiicate posteriorly l)y a chink with the dorsal 

 vessel on the œsophagus. The dorsal vessel runs down till it com- 

 numicates with the ventral vessel at the juncture of the stomach 

 and the intestine, by means of a small ring sinus. Anteriorly also 

 the dorsal vessel gives off two l)ranches which, after j^^i^^iwg" along 

 the inner side of the t\v(j notochords, again meet together in the 

 mid-ventral line, forming a post oral ring sinus. From that meeting 

 point originates the ventral vessel which nnis down along the 

 whole length of the gut and opens into a large sinus-ring situated 

 just within the perianal l)elt. Further, the author denied the free 

 conmumicatioii of the blood vessels with the body-cavitv, which 

 had been maintained by Metschkikoff and Caldwell. 



I have already stated my belief that the mother cells, of l)lood 



