132 LACINULARIA SOCIALIS 



vibrating with a quick undulatory motion in its cavity (fig. 8). As 

 Siebold remarks, it gives rise to an appearance singularly like that of 

 a flickering flame. 



I particularly endeavoured to find any appearance of an opening 

 near the vibratile cilium, but never succeeded, and several times I 

 thought I could distinctly observe that no such aperture existed. 

 Animals that have been kept for some days in a limited amount of 

 water are especially fit for these researches. They seem to become, 

 in a manner, dropsical, and the water-vessels partake in the general 

 dilatation. 



The " band " (fig. 7) which accompanies the vessel appsared to 

 me to consist merely of contractile substance, and to serve as a 

 mechanical support to the vessel. It terminates above, in a mass 

 of similar substance, containing vacuolse, attached to the upper plate 

 of the trochal disc. I shall refer to this and similar structures below. 



I examined these structures so frequently that I have no doubt 

 that the account I have given is essentially accurate,^ and I am 

 strengthened in this opinion by the account and figure of the corre- 

 sponding vessels in Mes-ostoinum given by Dr. Max Schulze, in his 

 very beautiful monograph upon the Turbellaria (Beitrage zur Naturges- 

 chichte d. Turbellarien). Through these the transition to the richly 

 ciliated water-vessels of the Naidae, &c., is easy enough. 



Vacuolar Thickenings. — (figs. 2, 3 r). Under this head I include 

 a series of structures of, as I believe, precisely similar nature, which, 

 on Professor Ehrenberg's principles of interpretation, have done duty 

 as ganglia, testes, &c., in short, have taken the place of any organ that 

 happened to be missing. 



In various parts of the body the parietes have become locally 

 thickened, and the prominences thus formed have developed many 

 clear spaces, or vacuolse — a histological process of very common 

 occurrence among the lower invertebrata. 



^ Leydig's careful description coincides in all essential points with that given above. He 

 particularly notices the fitness of Lacinularite that have been imprisoned for some time, for 

 the examination of the water-vascular system. 



The only discrepancy of importance in Leydig's account is — firstly, that he considers 

 what I have called the "vacuolar thickening on each side of the pharyngeal mass," and what 

 Ehrenberg calls a nervous centre, to be formed by convolutions of the water-vessel itself; 

 and secondly, that he describes a cloacal vesicle as in other Rotifera. I looked particularly 

 for such a vesicle, but could never see any ; in some cases, indeed, I could trace the water- 

 vessels distinct from one another, close to the anus. 



Beyond these particular cases, however, I will by no means venture to contradict so 

 accurate an observer as M. Leydig. 



Leydig does not seem to have noticed the transverse anastomosing vessel over the 

 ]jharynx. 



