OF THE ROTATOUIA. 427 



nective tissue. For instance, the intercurrent fibres about the head and neck 

 of the Eotatoria, and the interlacing cords passing forward to the lobes of 

 the rotary organ, and backward to the maxillarj head, were reckoned parts 

 of the vascular system. 



The purpose of a circulatory system is to convey the blood (the nutritive, 

 reparative fluid) within the reach of every tissue and organ, so that all its 

 parts may be renovated, and their effete, worn-out particles removed. The 

 necessity for such a contrivance is at once intelligible in large animals, where 

 the parts have considerable size and thickness, and are pretty closely packed 

 within the limits of the body ; but in the case of the Rotifers, the proto- 

 plasmic fluid fills up all the large space within the body unoccupied by the 

 \dscera, and is in immediate contact with them, whilst none of them have 

 such a density or thickness as to preclude their being readily permeated by 

 it. The result of digestion within the ahmentary canal is the production of 

 a nutritive juice or chyle, which apparently passes by exosmosis through the 

 walls of the canal into the general cavity of the body, mixing there with that 

 already existing, and is the representative of the blood of higher animals. 

 But, in addition to this, a constant renovation of the chyhferous liquid of the 

 body, by Avater taken in from without, appears to be necessaiy. 



Ehrenberg witnessed a periodical transparency in the body, with, an alter- 

 nating distension and collapse occurring regularly in almost all Rotatoria. 

 During distension, the outline of all the viscera seemed clearer, whilst, upon 

 the collapse, the organs approximated their limits, became less defined and 

 somewhat confused, and the integiunent crumpled. These movements he attri- 

 buted to the alternate entrance and exit of water from without, through the 

 medium of the supposed siphon tube on the head, or of oj)enings upon other 

 parts of the body. It has, however, been shown that the siphon and apparent 

 openings have no external commimication ; we must consequently believe, with 

 Ley dig, that the imbibition and exudation must be, in great measure, the 

 result of endosmotic action, — not forgetting, however, the influence w^hich is 

 necessarily exerted on the alternate movements in question by the action of 

 the respiratory apparatus to be presently described. 



Leydig remarks that " the mingling of the sanguineous fluid Tvith water 

 from without seems, at first sight, extraordinary ; it is, however, a fact in 

 physiology, founded on direct obsei-vatiou, Yan Beneden having detected it 

 in marine Mollusca, myself in Paludina vivipara, and, more recently, Gegen- 

 baui' in Heteropoda and Pteropoda.'^ The nutritive or sanguineous fluid of 

 the Rotatoria is, as a rule, clear and colourless, but in some species it has a 

 red or yellowish hue, e. g. in Notommata centrura, Synch(eta, and Polyarthra ; 

 it is, moreover, usually destitute of distinct floating particles or elements : 

 exceptions occiu- in Eospliora Najas, Eucidanis, and a few others, in which 

 small clear corpuscles move about in it just as in the blood of Annelida. '' Such 

 genuine elements," continues Leydig, " of the circulating fluid must, however, 

 not be confoimded with the Tuinute particles which at times detach themselves 

 from the tissues mthin the body and float about in the liquid. Such false 

 corpuscles are not uncommon in animals which have been partially crushed 

 or left diy by evaporation ; those noticed by Ehrenberg in Hydatina senta 

 were, in all probability, of this accidental kind." 



Dr. Dobie has recorded an observation of seemingly genuine moving cor- 

 puscles, which deserves a place here. He found, *' immediately below the 

 integument of Floscidaria cornuta, groups and lines of very small granules 

 continually in a state of rapid molecular motion, in appearance exactly resem- 

 bling the molecules in the cusps of Olosterium. Besides the molecular, they 

 are subject to another motion ; for occasionally they move from one part of 



