2060 Journal of Applied Microscopy 



Beard, J. The Numerical Law of Germ Cells. There are, broadly speaking, two alter- 

 Anat. Anz. 21 : 189-200, 1902. natives as to the relationship of a set 



of germ cells and an embryo : 1. The 

 embryo may have formed the germ cells. 2. The germ cells existed first and the 

 embryo arose from one or more of them. Hence the embryo is a development 

 of one primary germ cell for the purpose of guarding a certain set of germ cells 

 during a portion of their life cycle. 



The enumeration of germ cells gives added importance to the latter point of 

 view. It is soon seen that the number is a constant for the individuals of any 

 species, and it varies with different species. This number may be called 2". 

 There is often a disparity between their arrangement in the two halves of the 

 body, also in the total number of normally placed functional germ cells. In Raja 

 batis (the form especially studied), the germ cells must migrate into the embryo. 

 This causes a certain amount of irregularity in distribution. By rearing many 

 thousands of Elasmobranch embryos the writer tested this point. Surprisingly few 

 abnormalities occurred, but these few on examination showed many interesting 

 peculiarities in the distribution and number of germ cells. 'This is probably a 

 consequence from, not a cause of, the abnormality. A summary of five embryos 

 as to normally placed germ cells is as follows : 



No. of Embryo. Left Side. Right Side. 



742 None Normal 



743 Normal Few 



744 1 None 



745 Normal 4 



746 14 46 



There is great irregularity in distribution, in some cases the germ cells are 

 present in the defective side of the body and absent in the apparently normal 

 one ; in some the cells are all abnormally placed and in others a few in each 

 case. The aberrant cells occur in all places. They are some of them very 

 large, the megaspheres, equivalents of 8, 4, or usually 2 germ cells. 



Enumeration of the germ cells in embryos of Raja batis showed two numbers 

 near which the total always came. They were 512 or half of it, 256. These 

 are shown to correspond to the two sexes, the more numerous the female, the less 

 the male. 



The following forms were also investigated and 2" being assumed as repre- 

 senting the number, the actual figures are shown to vary from 8 to 512 in the 

 different animals : Ra/ia esculetita ^, Peiromyson p/aneri ^^2, Acanthias vulgaris 

 64, Scyl/ium caiiicula 128, Raja batis 256, Raja batis 512. Thus all powers of 2 

 from 2^ to 2^ excepting 2^ are seen. From this total must be deducted that 

 number of cells that goes to form the embryo. This makes the formula for any 

 given Metazoan to be 2" — 1. It should be borne in mind that the two symbols 

 2" and 2^^ — 1 have recently been used in a different but equally significant 

 sense by the late Gregor Mendel. a. m. c. 



