199 



still be outside of the embryo. The normal number here is concluded 

 to be about 64(?). 



To the foregoing may be added a few counts made in Rana escu- 

 lenta and Petromyzon planeri. In two cases of the former 7 primary 

 germ-cells were counted, in three of the latter 3i. 



The following numbers have thus been more or less exactly ob- 

 tained: 



Rana esculenta i) 



Petromyzon planeri 



Acanthias vulgaris 



Scyllium canicula 



Pristiurus melanostomi 



Raja batis (J 



Raja batis 5 



Add to these from the literature: 



(Haecker) Cyclops 

 (BovERi) Ascaris 

 (Metschnikoff) Cecidomyia 2n 

 (Ritter) Chironomus 2n = 8 



Other well-known cases might have been cited, but for some doubt 

 as to the actual number of germ - cells recorded, or if any statement 

 at all had been made as to their number. 



In this short list, embracing representatives of widely separated 

 groups, though unfortunately of nothing like all, every power of 2 from 

 21 to 29, with the sole exception of 24, is included. 



The conclusion drawn is, that the number of primary germ- 

 cells in any Metazoan development is 2^. 



But from considerations, into which I have entered elsewhere-) 

 more fully, i. e., concerning like- twins, the equivalence of the primary 

 germ-cells in any given case, and the facts of the development them- 

 selves, this does not represent the largest actual number of primary 

 germ-cells to be found in any given embryo. In every case the pri- 

 "mary germ-cell, sacrificed to form the embryo, must be deducted, and 

 thus the actual law comes to be: 



1) 2n = 8, but 2n— 1 = 7, so also for the lamprey, where 2n = 32, 

 but 2n— 1 = 31. 



2) J. Beard, Heredity and the Epicycle of the Germ-Cells (in the 

 press), in Biol. Cenfralbl., 1902. This paper was read before the 

 Botanical Society, Edinburgh, on 7th Jan. 1902. In it will be found, 

 among other things, the sequel to the present writing, the "Understudy- 

 Theory of Heredity ". 



