110 SEA-SIDE STUDIES. 



noted on this point. Owen and Siebold assured me that I was 

 right in denying the Eolids anything properly to be styled a 

 gill. The former says : " In certain small shell-less marine 

 genera — e. g. Rhodope, Tergipes, Eolidina — no distinct 

 respiratory organs have been detected ; these form the order 

 Apneusta." Professor Owen enters into no details ; he 

 simply asserts the fact, that no distinct organs exist. Sie- 

 bold follows Kolliker, who establishes the order Apneusta, 

 " in opposition to the other Gasteropoda, which have dis- 

 tinct respiratory organs/' But the only reason adduced by 

 him seems to me far from cogent; and I can understand 

 how Alder and Hancock, who must have been perfectly aware 

 of the position taken by Kolliker and Siebold, might alto- 

 gether disregard it. Siebold says that the opinion respect- 

 ing the branchial nature of the papillse " is untenable, since 

 it has been shown that they contain prolongations of the 

 digestive canal."* I believe it to be untenable, simply 

 because the papillae contain none of the distinctive characters 

 of gills ; did they possess these, the fact of their also con- 

 taining digestive prolongations would not deprive them of 

 their rank as gills ; any more than the fact of the heart, in 

 some Molluscs, allowing the intestine to pass through it, 

 deprives it of cardiac dignity. 



Quitting this discussion for topics more surprising, let us 

 fix our attention on one fact, cursorily indicated on a preced- 

 ing page, namely, the existence, in the foot of the DoHs, of 

 a system of pores through which the water enters into the 

 general cavity of the body. It is a fact which has not 



• Siebold— Com/). Anat., English Ti-ans., p. 249. 



