200 



The number of primary germ -cells in any given Me- 

 tazoan development is 2", but with the sacrifice, en- 

 tailed by the development of one primary germ-cell to 

 form an embryo for the reception of the rest, the great- 

 est actual number of primary germ-cells in any embryo 

 will be 2n— 1. 



Finally, I would direct the reader's attention to the fact, that 

 in a diflerent, but equally significant, connection, the two symbols, 

 2n and 2ii— 1, have been set up by the late Gregor Mendel^). 



Nachdruck verboten. 



On the Presence of a Crystalline style and style-sac in 

 Turritella communis. 



By W. B. EaxNdles, B.Sc. 



(Erom the Zoological Laboratory of the Royal College of Science, London.) 



With 3 Figures. 



In a short account of the anatomy of Turritella communis 2) 

 which I published in 1900, very little importance was attached to the 

 presence of a distinct median constriction dividing the stomach into 

 anterior and posterior chambers; and though several stomachs were 

 opened, the occurrence of a crystalline style-sac was entirely over- 

 looked. The specimens examined were not in a good state of pre- 

 servation, the upper whorls together with the stomach being partially 

 macerated. Some time after the publication of the above paper, 

 several living specimens of Turritella were obtained, these were 

 carefully preserved, the shells having been previously removed. 



It was, however, only quite recently at the suggestion of Mr. 

 J. E. S. Moore, that a re-examination of the stomach of this form 

 was made, for the purpose of ascertaining whether a crystalline style 

 was present or not. On opening the stomach from the outer con- 

 vex side, a moderately large crystalline style was found in the 



1) Gregor Mendel, Versuche über Pflanzenhybriden, Ostwald's 

 Klassiker d. exacten Wissenschaften, no. 121, p. 17. See also Batesün's 

 translation in Journ. Roy. Hort. Soc, Vol. 26, 1901, p. 12. 



2) W. B. Randles, Anatomy of Turritella communis Risse. Proc. 

 Malac. Soc. Lond.. Vol. 4, Part 2, August 1900. 



