122 CHlury Motions in Reptiles and Wann-hlouded Animals. 



tious, when this is used to avoid being deceived by the molecu- 

 lar motion described by Brown, which the particles of pigment 

 exhibit in a remarkable degree. Blood sufficiently diluted may 

 also be employed for the same purpose. The current of these 

 particles along the margin of the fold is so strong as to strike 

 the most unpractised eye. 



Some additional precautions are, in certain cases, rendered 

 necessary by the nature of the tissue. It is in all cases abso- 

 lutely necessary that the mucous membrane alone should be em- 

 ployed. Hence no portion of muscular coat, or of bronchial 

 cartilage, must be left adhering to it, otherwise the observation 

 is not merely impeded, but entirely frustrated. 



On account of the peculiar structure of the lungs of reptiles, 

 the following circumstance must be attended to in their exami- 

 nation. The interior of these organs presents a number of con- 

 tiguous cells, whose parietes are united with one another in an 

 elegantly reticulated manner; if a portion of such a lung be fold- 

 ed in the way prescribed, the mucous membrane of these cells 

 will, for the most part, be still concealed, and its free surface 

 will be exposed only in a few places ; hence it is in such places 

 alone that the motion is to be looked for. 



c. Nature and Character of the Vibratory Motions. 



The vibratory motions are extremely rapid motions which ap- 

 pear on the surface of the parts, the eye being scarcely able to 

 follow their particular features, when viewed in their most vivid 

 state. Wherever they occur, they observe, like the currents which 

 they excite, a determinate direction ; we have met with only one 

 exception to this rule, namely, in the appendages of the gills of 

 the river mussel, in which th^ movements went alternately in two 

 different directions in a regular manner, the change of direction 

 taking place every six or seven seconds. In all other cases, 

 however, the movements, whatever their degree of vivacity, 

 maintain invariably the same direction. 



From our observations, it seems highly probable that the vi- 

 bratory motions are always produced by cilia; for, as will be 

 more particularly stated on another occasion, we have found 

 evident traces of them even in the larvae of the Batrachia. In 



