126 ROTIFERA. 



seven vibrating points on one side, and six on the other, attached 

 to two long and undulating viscera, (/, /,) which he elsewhere 

 describes as being the testes of the animal : the above-mentioned 

 points were never at rest, and appeared to be placed in determinate 

 positions opposite to each other. Accurate observations, he says, 

 have shown each to be a peculiar little organ, provided with a tail 

 resembling that of a note in music, and to be thrown into vibration 

 by three little vesicles or folds of their inflated extremity ; these 

 organs floated freely in the abdominal cavity by their enlarged 

 portion, while by their tail they were attached to the long tubular 

 organ above referred to (figs. 49 and 50). 



Ehrenberg's first idea, on seeing these organs, was, that they 

 formed a vascular system, executing movements of pulsation ; but 

 he now considers them as internal branchiae, or organs of respira- 

 tion, to which the external water is freely admitted in the following 

 manner. 



In many species of the rotifera, we find, projecting from the neck 

 of the animal, a horny tubular organ, called by Ehrenberg the Calcar 

 or spur (figs. 49 d, and 50 Z>) ; this he at first considered to be 

 the male organ of sexual excitement, but he now regards it as a 

 syphon or tube of respiration, through which the circumambient 

 water passes freely into the cavity of the body. He thinks, more- 

 over, that the periodical transparency, and the alternate distension 

 and collapse of the animal, seen to occur regularly in almost all the 

 Rotifera, are produced by the introduction of water into the visceral 

 cavity, and its subsequent expulsion therefrom, upon which action 

 the fluctuations observed in the interior of the body would there- 

 fore depend. The supposition that water is injected in this 

 manner into the body seems to be favoured by other appear- 

 ances ; for, when the internal cavity is thus filled, all the viscera 

 appear isolated, so that the boundaries of each can be distinctly 

 seen, but when the water is discharged they approximate each 

 other, their limits become confounded, and the external membrane 

 of the body assumes a crumpled appearance. 



Upon reviewing the above account of the mode of respiration in 

 the rotifera, we must say that we consider that the office assigned 

 to the little organs called internal branchiae is extremely proble- 

 matical, especially as we have but the most vague intimations con- 

 cerning the existence of a circulating system at all, much less of 

 such a double circulation carried on in arteries and veins as the 

 presence of such organs would infer. " I presume," says Ehrenberg, 



