452 notp:8 on phosohhanciuata. 



IS. — HvATT, A, — "The Terms of ' Bioplastology,' 'Ontogeny.'" Zoolo- 



gischer Anzeiger No. 427, 1S98, p. 82"). 

 19.— Jacksox. — "Phjlogeny of the Pelecypoda." Memoirs Boston Soc. 



Nat. Hist. iv. No. 8, 1890, p. 290. 



Postscript. — After tliis paper was read Mr. C. Hedley drew 

 my attention to a paper by Dr. Willey,"^ " On the Nepionic Shell 

 of the Recent Kmifihts," in which the author regards the date of 

 hatching as the date of the conclusion of the nepionic stage. 

 He says : — " Thus the nepionic shell of the (' terrestrial Gastero- 

 pod ') molluscs is that portion of the true shell (as opposed to the 

 embryonic shell), which develops within the egg." This, I ven- 

 ture to suggest, is a misinterpretation of the term. If we accept, 

 as we must, Dr. Jackson's definition of the Molluscan phylembryo 

 as the veliger and last embryonic stage; and if the velum becomes 

 aborted within the egg, however quickly; then that stage during 

 which this "larval organ " is aborted, must, as in other cases, be 

 recognised. Thus, such a mollusc, terrestrial or otherwise, has 

 already entered upon the neanic stage before leaving the egg. 

 Some Anuran Amphibia are hatched in the adult form, but we 

 do not regard them as tadpoles, because most of the Anura are 

 hatched as tadpoles. We cannot say what stage of development 

 Nautilus is hatched in, so that the shells discussed by Dr. Willey 

 in the paper referred to may be rightly termed "nepionic"; on 

 the other hand they might equally well be neanic (t^eptemher 2ofhy 

 190S). 



* Willey, Quart. Journ. Microseop. Sci., xxxix., pp. 222-230, 1897. 



[Printed oft' September 30th, 1903. 



