LACINULARIA SOCIALIS 131 



Other end. A spiral vessel, closed at the extremity, runs through 

 most of its length, which maintains a wavy motion " — p. 98. ^ 



The following is what I have seen in Lacinularia : — There is no 

 contractile sac opening into the cloaca as in other genera ; but two 

 very delicate vessels, about i -4000th of an inch in diameter, clear and 

 colourless (fig. 3 ;;/), arise by a common origin upon the dorsal side 

 of the intestine. Whether they open into this, or have a distinct 

 external duct, I cannot say. 



The vessels separate, and one runs up on each side of the body 

 towards its oral side (fig. 2). Arrived at the level of the pharyngeal 

 bulb, each vessel divides into three branches (fig. 3) ; one passes over 

 the pharynx and in front of the pharyngeal bulb, and unites with its 

 fellow of the opposite side, while the other two pass, one inwards and 

 the other outwards, in the space between the two layers of the trochal 

 disc, and there terminate as coeca. Besides these there sometimes 

 seemed to be another branch, just below the pancreatic sacs. 



A vibratile body was contained in each of the coecal branches ; 

 and there was one on each side in the transverse connecting branch. 

 Two more were contained in each lateral main trunk, one opposite 

 the pancreatic sacs, and one lower down, making in all five on each 

 side. 



Each of these bodies was a long cilium (i-i400th of an inch), 

 attached by one extremity to the side of the vessel, and by the other 



1 M. Udekem (Annales des Sciences, 1851) has given a very elaborate, but I think not 

 altogether correct, account of the water-vascular system of Lacimtlaria. He says that a 

 vascular network exists at the base of the lobes of the wheel-organ ; that these unite 

 into gland-like ganglia (my "vacuolar thickenings," in the margin of the disc infra); 

 that from these vessels proceed to the central glands (vacuolar substance, in which the 

 " band " of the water-vascular system terminates, ««7iz'), from which three great vessels are 

 given off. Of these, one " passes above the digestive tube, and anastomoses with its fellow 

 from the opposite ganglion ; the second presents the same disposition as the first, but is 

 placed below the digestive tube ; the third passes directly downwards, skirting the digestive 

 tube"; M. Udekem found it "impossible to trace it any further, but considers that it 

 becomes lost on the digestive canal and ovaries." He, therefore, has missed the external 

 opening of the water-vascular system. 



What I have seen and described as "vacuolar thickenings" in the peduncle, are described 

 by M. Udekem as vascular ganglia, from which anastomosing vessels proceed. 



As M. Udekem's instrument does not seem to have been good enough to define the 

 vibratile cilium — for he speaks only of a "vibratile or trembHng movement" — I venture to 

 think that he has been misled in describing these threads and vacuolar thickenings as forming 

 any part of the true vascular system. 



Leydig's opinion of M. Udekem's results is, I find, much the same as my own. He says, 

 " Critically considered, then, we find that Udekem's vascular system in Lacinularia is 

 compounded of a multitude of the most heterogeneous parts of the animal— of structures 

 which belong to the most different systems of organs, without one being a true blood-vessel." 

 — Loc. cit. p. 455. 



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