137 



a vessel nearly totally separated from the intestinal blood sinus '^ ; how- 

 ever it only can be proved by studying the development of these Anne- 

 lids, whether we have to do with a secondary vessel or with the homo- 

 logue of the typical dorsal vessel. 



My interpretation of the morphological value of the heart of Chlo- 

 raemidae was based upon facts, furnished by the comparative Anatomy 

 as well as by the Embryology of the Annelida. I argued that the worms, 

 belonging to the family of Enchytraeidae, have a free dorsal vessel only 

 in the anterior segments, in connection with a blood-sinus around the 

 intestine in the posterior segments of the body, whereas in the allied 

 families there exists a free dorsal vessel over the total length of the 

 body. ^Moreover it results from Mr. Salensky's researches on the 

 development of Terebellidae — which, according to Mr. Edwards''' 

 investigations, should have in the adult state a free dorsal and a ventral 

 vessel — that the vascular system in the larval state is only represented 

 by an intestinal sinus between the entoderm and the splanchnic layer. 

 The vessels at the dorsal and the ventral side of the intestine, as stated 

 by Salensky'', derive from the splanchnic layer, being first a gutter- 

 shaped canal, and afterwards becoming a completely closed vessel. I 

 thought it was permitted to conclude from these facts, that the vascular 

 system of the Enchytraeidae and of Brada has maintained an embryo- 

 nic arrangement. About this view Mr. Cunningham says: «Horst's 

 remark, that the presence of a free dorsal vessel in the anterior somites 

 only, is merely embryonic in Terebellidae, is far from correct; in Tere- 

 bellidae, Ampharetidae and Amphictenidae namely an anterior heart 

 similar to that of the Chloraemidae is present, and its posterior end is 

 connected with a blood-sinus in the walls of the intestine, which is 

 the only representative of the typical dorsal vessel.« 



Of course there exists in these families an intestinal sinus not only 

 in the larval state (as stated by me) , but also in the adult condition. 

 I believe Mr. Cunningham's attack of my vicAvs is not very fair. 

 In the beginning of the year 1885, when I published my Note in the 

 Zool. Anz., our knowledge of the vascular system of the Terebellidae 

 was based especially upon the researches of Mr. Edwards; their 

 exactness had been confirmed by Claparcde, whose authority in 

 matter of anatomy of Annelida, in my opinion, counts for much. In 

 his beautiful Avork: »Les Annélides Chétopodes du Golfe de Naples« 



■5 Mr. Wir en in bis »Beiträge zur Anatomie und Histologie der limivoren 

 Anneliden« p. 43, kindly forwarded to me just now, appears to have the same opinion. 



6 Recherches pour servir à l'histoire de la circulation du sang chez les Anné- 

 lides. Ann. Sc. Nat. 2e Scr. T. X. p. VXi. 



7 Arch, de Biol. T. IV. p. 252. 



