CH. II] THE CRAYFISB 65 



advantage be extended to similar structures in other 

 invertebrate and vertebrate animals. 



True, it has been shown that the "auditory" setae 

 of some Crustaceans are thrown into vibration by certain 

 noises and musical notes, but this does not prove that they 

 give rise to the sensation of hearing. A loud noise will 

 throw many of the wires of a piano into vibrations and 

 cause them to give out their respective notes. Similarly 

 these " auditory " setae will undoubtedly respond to their 

 appropriate notes, but it seems unreasonable to infer on 

 that account that they are sense organs for the perception 

 of waves of sound. 



Crayfish undoubtedly possess a sense of smell : this 

 sense has been attributed to the flattened spoon-shaped 

 setae found on the ventral surfaces of the more distal joints 

 of the outer branch of the first antenna. It is interesting 

 in this connexion to note that when the animal is at rest 

 or slowly advancing the outer branch is always held up, 

 pointing obliquely forward, and from time to time is jerked 

 downwards and up again. The inner branch is held 

 horizontally 1 . 



It is probable that the setae which occur scattered over 

 the general surface of the body and especially upon the 

 antennae are sensory (tactile ?) in function. 



Reproduction, Development, and Regeneration. In 

 September or October the ventral surface of the abdomen 

 of the female crayfish assumes a white appearance due 

 to the activity of certain cement glands, situated in the 



1 Cf. Boas, Morph. Jahrb. vin. p. 490 ; Jourdain, G. R. Acad. Sci. Paris, 

 xci. p. 1091 ; and Jour, de VAnat. xvn. ; Leydig, Miiller's Arch. 1860. 



