51 



the smooth skate. Although quite ready for the press in July 1900, 

 the publication has been delayed for cogent reasons. From the various 

 enumerations of the germ-cells of this fish it was clear to the writer, 

 that some numerical law underlay the matter, and that possibly a 

 numerical difference obtained between the germ - cells in potentially 

 male and female skate. The working-out of the actual "Numerical 

 Law of the Germ-Cells" and of the problem of the existence of four- 

 fold gametes as underlying the phenomena of sex have naturally re- 

 quired a considerable interval of time. 



The embryos studied and the germ-cells enumerated and tabulated, 

 wherever possible, during the past working year include a large number 

 of Raja batis, a few R. radiata, 17 Pristiurus malanostomus, 8 Scyl- 

 lium canicula, a small set of Torpedo ocellata, a few of Acanthias 

 vulgaris, a number of chicks of various periods, and, lastly, a few 

 examples of Rana esculenta, and Petromyzon Planeri. 



Detailed accounts of as many as possible of these will be given 

 in a forthcoming memoir on the germ -cells; for the original work, 

 dealing with the skate alone, has now extended itself into a com- 

 parative account of germ-cells in general. 



The Germ-Cells of Pristiurus^). 

 For three reasons this form has been included within the sphere 

 of the observations. It is, thanks to the Zoological Station ,of Naples, 

 an accessible form, and numbers of its embryos are already in the 

 possession of various embryologists. It was also the form studied by 

 the most recent investigator, C. Rabl ('96), of the development of 

 the " germinal glands " of Elasmobranchs, and in view of discrepancies 

 between his results in Pristiurus and mine in Raja it seemed desirable 

 to inquire into the actual facts. Moreover, at the time of writing my 

 former paper I was aware from^the tabulation of the germ-cells of a 

 single embryo of the former, that, at a certain period at any rate, 

 there might be as large a percentage as 12 ^/o in abnormal or im- 

 possible situations in Pristiurus. Lastly, it was taken up as an ad- 

 ditional form for enumerations of the germ-cells. 



1) My thanks are due, and may be here expressed, to Herrn Geb. 

 Regierungsrat Prof. Dohrn for his generosity in placing at my disposal 

 a large number of embryos of this form, the total embracing more than 

 100 embrj'os of all periods up to 30 mm or thereabouts. The limited 

 number here made use of is due to 1) lack of time, 2) the circum- 

 stance, that this communication is not designed to be a complete history 

 of the germ-cells of Pristiurus, and 3) the fact, that the number as yet 

 examined is sufficient for present purposes. 



4* 



