Natural History of Molluscous Animals. 235 



tubercles, pointing apparently to the mouth. From this 

 aperture a cylindrical tough proboscis may be extruded, 

 nearly equal to the body in length, swelling towards the apex 

 into a bulb, armed behind with retroverted spinules, and the 

 aperture itself encircled with numerous short and thickish 

 tentacula. When the body is compressed between plates of 

 glass, the alimentary canal is seen proceeding straight to near 

 the middle, where it forms a considerable flexure, and thence 

 it has a convoluted course towards the posterior extremity, 

 when it returns upon itself, and opens outwardly at the base 

 of the proboscis. No trace of any other organ is visible. 

 There are three small anomalous appendages at the posterior 

 end, the nature of which I do not understand. 



When the larger tubercles that encircle the central part of 

 the body are magnified (d), they seem to be suckers or cups, 

 not unlike the cups which are placed along the arms of the 

 cuttlefish, but the shape is probably somewhat altered by the 

 pressure to which they were subjected between the glasses. 



The greater number of systematic authors have placed the 

 Siphunculus amongst the radiated animals near the genus 

 Holothuria; but De Blainville has removed it from that class, 

 to place it among the true worms. The propriety of this, if I 

 may be permitted to give an opinion, is very doubtful, for the 

 existence of the tentacular circle at the oral aperture seems to 

 indicate some kindred to the radiated tribes ; and its affinity 

 to the Holothuria will be made still more apparent, if my 

 observation, that the seeming tubercles are in reality suckers, 

 is confirmed. 



Berwick upon Tweed, February 23. 1833. 



Art. XIII. An Introduction to the Natural History of Molluscous 

 Animals. In a Series of Letters. By G. J. 



Letter 11. On their Organs of Respiration. 



The respiratory organs of the Mollusca have peculiar 

 claims to the attention of the conchologist, not solely because 

 of their function, which, indeed, is one of chief importance, 

 but because they have furnished the principal characters 

 on which modern systematists have proceeded to subdivide 

 the class into orders and families. Cuvier, of whom, among 

 recent naturalists, it may most truly be said that he was 



" Ordain' d to light with intellectual day 

 The mazy wheels of Nature as they play," 



