Branchial Organs of the Infusoria, 59 



on one side only, which made it resemble the combs which scor- 

 pions carry under the belly. These clubs and their vessels are 

 so small, and so clear, like the purest crystal, that it is almost 

 impossible to perceive them, except when the animal is in mo- 

 tion ; but when once seen, they may always be distinguished 

 very plainly. Only one of these organs has hitherto been dis- 

 covered. As the small clubs are very numerous and very com- 

 pact, it is probable that no more exist. 



It is expected of him who discovers an organ, that he will 

 give an account of its relations with the other parts of the ani- 

 mal ; and the method which our author took to accomplish this 

 object was the following : — The observations to which we have 

 been just alluding, led him to return to an external organ, 

 which has been formerly mentioned, and of which he then did 

 not know the function, viz. the spur which is found at the neck 

 of a great number of the Rotatoria. At first he had supposed 

 that this spur was an existing organ of the sexual system, be- 

 cause it resembled in its situation and form the penis of the 

 univalve Moll u sea. But even in his second dissertation, he had 

 demonstrated in detail that this organ has no connexion with the 

 internal sexual parts : and this it was which induced him to 

 substitute the term spur for that of chtoris. Now, when he 

 connects his former observations concerning the fluctuation in the 

 abdominal cavity of the Rotatoria, to what he has established 

 concerning the crooked organ which is placed upon the neck, 

 and also to that which he has established concerning the vibra- 

 tory organs attached in a line to the sides of the interior of the 

 body, he cannot hesitate to consider all these parts as forming a 

 very distinct respiratory apparatus. He regards the spur as a 

 syphon, or respiratory tube, and believes that the periodic trans- 

 parence, the extension and subsequent subsiding of the body, 

 which almost regularly takes place in all the Rotatoria, is the re- 

 sult of the introduction of water into the internal cavity of the 

 body. The fluctuations which he had observed in the interior 

 of the body would then become the moving of this water. When 

 the internal cavity of the body of these Rotatoria is thus filled, all 

 the internal organs appear isolated, so that their limits are seen 

 very distinctly ; but the water being evacuated, which may be ex- 

 cellently seen in the Hydatina senta, they, on the contrary, ap- 



