FORM OF NEPHRIDIA IN ARENICOL1D.E. 2$ I 



other Poiychata, (see Fraipont on Poygordius, for instance), as 

 well as in the OligocJiceta (Wilson on Lumbricus), the first vessel 

 to arise as a differentiation of the mesoderm, is the ventral vessel. 

 Wilson says " The first vessel to appear (in Lumbricus] is the 

 ventral or sub-intestinal." What the relation of this first vessel 

 genenally is to the development of the circum-intestinal network 

 in the polychaets is an unsettled point. (See Edward Myer's 

 " Studien iiber den Korperbau der Anneliden," III., p. 464.) 

 Recently Schiller writes as follows : " Nur bezuglich Blutsinus 

 und Darmgefasznetz ist mann bei Arenicola GmbH noch nicht ins 

 klare gekommen, welches von den beider das primare sei, da 

 verscheidene Autoren ganz verscheidener Ansicht daruber sind. 

 Die einer behaupten dasz zuerst der Sinus auftrete und sekundar 

 sich in ein Netz auflose : die anderen bezeichnen den Blutsinus 

 als ein Produkt des zusammengeschmolzen Darmgefasznetzes." 

 He does not care to express an opinion on the subject although 

 of the growing posterior region of A. GmbH he says : " Im 

 Darmepithel keine besonderen Zellen vorkommen, die Antrit an 

 der Bildung eines Sinus nehmen konnten." In considering der 

 Blutsinus, Darmgefasznetz und Subintestinalgefasz he says : " Diese 

 drei Gebilde werden hier zusammen als anatomisch und entwicke- 

 lungsgeschichtlich zusammengehorende Elemente." 



I have taken pains to quote in order to show that in spite of 

 the difference of opinion regarding the origin of the network of 

 intestinal vessels there is no tendency to include the ventral vessel 

 in Arenicola or other polychaets as a part of this network which 

 does, however, include the subintestinals. In A. marina we 

 know (Benham, 1893) that the subintestinal vessels and the 

 gastric longitudinals develop as the result of a fusion of the walls 

 of the circular vessels of the alimentary canal. While in the 

 oligochaets the subintestinal vessels split off from the ventral 

 vessel. (Beddard, F. E., "Monograph of the Oligochaeta," p. 

 70.) The term subintestinal vessel is an incorrect term for the 

 vessels so named in Arenicola. Lillie should not have used the 

 term subintestinal when he meant ventral, as these two terms are 

 not interchangeable in Arenicola. The ventral vessel or subin- 

 testinal vessel of Lumbricus they remain united in this form - 

 is not homologous to the ventral plus the subintestinal vessels of 

 Arenicola. 



