TUBIFEX KIVULORUM. 19 



joining the dorsal, could not be determined." The foregoing 

 account of Dr. Mcintosh is in the main confirmatory of the 

 observations of Claparede, some additions being made thereto. 

 It will be observed that the " perivisceral branches " proceed 

 toward the body- wall, floating, as they do, freely in the perivisceral 

 cavity ; while the others, which proceed from the ventral main 

 trunk, tightly enclose the intestine ; they are called by Claparede 

 the " intestinal branches." The periviscerals of the eighth 

 segment appear to be slightly more swollen than the others, and 

 have been described as hearts, — a pulsating movement being 

 observed in them. The pulsations, however, do not appear to be 

 confined to those of the eighth segment, but extend, according to 

 Claparede, to the tenth, eleventh, and twelfth. I have myself 

 seen portions of these vessels suddenly contract and assume a 

 puckered aspect, the contained red fluid being completely, for the 

 moment, expelled. 



It may be observed that there are no special respiratory 

 organs visible in Tubifex ; and the question may be asked, in the 

 first place, " How is the respiratory process carried on ? " and in 

 the next, " Which of the two fluids in question is the subject of 

 that process?" The thinness of the integument would in any 

 case offer great facility for the aeration of the blood, and 

 especially in the intestine, where a constant access of fresh water 

 is maintained by ciliary action ; but the true answer to the 

 question would seem to be involved in considerable difficulty, from 

 the opposite points of view in which the relations of the two 

 fluids are regarded ; for while Dr. Williams, who regards the 

 circulating fluid as true blood, thinks that it receives its supply of 

 oxygen in great part through the intermediate agency of the 

 perivisceral fluid by which its vessels are bathed, — Dr. Carpenter, 

 on the other hand, regarding the perivisceral fluid as the true 

 blood, conceives that the coils of the " vascular system " floating 

 therein are destined to convey to // the aerating influence received 

 by the red fluid in its circuit. 



We must now notice the coiled vessels, which have received the 

 name of segmental organs. They are two in number on each seg- 

 ment (Fig. lo), and consist of long, twisted, vibratile canals, with 

 an external and an internal orifice. They are provided with an 

 external and an internal tunic, the former of which is described 

 by d'Udekem as elevated into pouches'^ (see Fig. 6), and the latter 

 is provided with cilia, which cause a current to flow from the 

 interior towards the exterior. The external orifice is situated a 



* I am doubtful as to the correctness of this observation. In Lininodrilus 

 Hoffmeisteri, Claparede describes the organs of the 7th and 8th segments as 

 covered with a mass of pyriform glandular cells (see Fig. 11), and I have been able 

 to verify his statement. Possibly, d'Udekem's pouches are also cells. 



