The determination of sex in animal development. 705 



were, and still are, believed to be produced from the tissues of these 

 said individuals, there could be but two forms of gametes, eggs and 

 spermatozoa. 



It is purely an assumption, that only two forms of gametes exist 

 in the Metazoa, an assumption, moreover, opposed to the actual facts. 

 In the following pages the writer adduces proof of the occurrence of 

 fourfold gametes, of which three are functional, in several instances. 

 All current views are based upon the existence of but two sorts of 

 gametes, and so sure have embryologists been of the truth of this, 

 that they have never attempted to establish it in fact 

 in any one case! 



The existence of whole genera, in which functional hermaphroditism 

 with the production of twofold functional gametes by one form of in- 

 dividual was the normal condition ought to have made it patent, that 

 the Metazoan individual differentiated two sorts of gametes. The er- 

 roneous conception of the original or primitive nature of herm- 

 aphroditism however, stood, stubbornly in the way of any such re- 

 cognition of the truth. 



The conclusions here presented are portions only of a picture — 

 the cycle of the development from one generation to the next : they are 

 a small, though important, chapter in the history of the germ-cells. 

 It may, therefore, help the reader, especially if he be not versed in 

 the embryology of the higher animals, if a brief epitome of the 

 writer's investigations and results concerning the course of the cycle 

 from generation to generation, as well as a few other details of the 

 story of the germ-cells, be given. A short account of the latter has 

 recently been published elsewhere ^), and to this and nos. 5 to 8 of 

 the list below the reader may be referred for fuller information. 



1) Beard, J., The morphological continuity of the germ-cells in 

 Raja batis, in: Anat. Anz., V. 18, 1900, p. 465 — 485. 



Other portions of the developmental cycle have been dealt with by 

 the writer in the following memoirs: 



1. On a supposed law of Metazoan development, in: Anat. Anz., 

 1892. 



2. The history of a transient nervous apparatus in certain Ich- 

 thyopsida, Pt. 1, Raja batis, with 8 plates, in: Zool. Jahrb., 

 V. 8, Anat., 1896. 



3. On certain problems of Vertebrate embryology, Jena 1896. 



4. The span of gestation and the cause of birth, Jena 1897. 



5. Heredity and the epicycle of the germ-cells, in: Biol. Ctrbl., V. 22, 

 1902. 



