4H NATURAL SCIENCE. June, 1895. 



relation to the posterior branchiae that the osphradia of Lankester and 

 Bourne have to the anterior branchiae. Their greater proximity to 

 the middle line is shared in common with the posterior renal sacs 

 and renal apertures, and even the posterior branchial veins, as com- 

 pared with the corresponding anterior structures. 



That they are bifid and, therefore, more highly developed than the 

 anterior osphradia, 11 is in keeping with their position in the living 

 Nautilus in the anterior region of the mantle cavity, and also with 

 the fact that the posterior branchiae, with which they would be 

 associated in the metameric system, are considerably larger than the 

 anterior branchiae. 



I remain, dear Professor Lankester, 

 Ralum, New Britain, Yours very truly, 



February 10, 1895. Arthur Willey. 



11 It must be remembered that the terms anterior and posterior as used above 

 refer to the reflected position of the mantle and not to the actual position in the 

 living animal. 



