The determination of sex in animal development. 717 



As I have elsewhere already insisted (in : Mitth. zool. Stat. 

 Neapel, V. 13, 1898, p. 304) hermaphroditism and parthenogenesis 

 are mutually exclusive. This may now be obvious. Similarly in the 

 animal kingdom males, females, and hermaphrodites do not and 

 cannot obtain within the limits of a species. 



IL The Gametes of the Metazoa. — The four Categories of 

 Grametes, and the three Kinds of functional ones — Pseudo- 



Hermaphroditism. 



The above are in brief form further conclusions, drawn from my 

 researches on the germ-cells. In part they are based upon certain 

 facts, disclosed in the course of the work; and in part they would 

 seem to be legitimate inferences from known facts, from the resolution 

 of the life-cycle into that of a unicellular organism, and from the 

 table of the life-cycle of the skate, published in the paper on „Heredity 

 and the Epicycle of the Germ-cells." 



From enumerations of the primary germ-cells of Baja hafis it 

 presently became evident, that the total always approximated more 

 or less closely to one or other of two numbers. It was either 256, 

 or double this, 512. These numbers of primary germ-cells cannot be 

 derived from germinal areas of like sizes. In the smooth skate 

 there must be "macro-eggs" and "micro-eggs" — exactly as in Dino- 

 philus apatris, Phylloxera, and Eydatina senta — for, whether there 

 be 256 germ-cells or 512, these cells are practically of the like 

 average size, 0,02 mm. This was found to be the case: the germinal 

 discs of segmenting eggs of the smooth skate are of two sizes ^). 



1) At present it cannot be stated whether or not this applies to 

 the yolk-mass also. Possibly it does not, for in both males and females 

 the embryo remains within the egg-capsule for the like period. But I 

 have long been struck by the fact, that in certain periods of the devel- 

 opment of R. batis there are obviously two sizes of embryos, thus in 

 embryos of 8 — 10 mm some embryos of the former size exhibit the 

 same degree of development as others of the latter dimensions, even 

 under the identical preservation. It does seem possible, that the marked 

 sexual dimorphism, so often obtaining among animals, e. g., Lepidosfeus 

 osseus, Cyclopterus lumpus, JBonellia, and Sacculina, may be in asso- 

 ciation with, and a consequence of, a considerable difference in the 

 number of primary germ-cells in the two sexes. 



From a fairly large number of exact measurements of large Maja 

 hatis, kindly made by my friend, Mr. P. Jamieson, in the fish-market 

 at Aberdeen, a small but constant difference in size between male and 



47* 



