The determination of sex in animal development. 737 



Aves: Larus, Tadorna (E. Ballowitz, 1890). 



Mammalia: The following by K. von Bardeleben: Ornitho- 

 rhynchus, Echidna, various Marsupials, and Erinaceus europaeus, and, 

 lastly, Homo sapiens (Fig. 1, von la Valette St. George, K. von 

 Bardeleben, von Widersperg). 



Spermatogonia of large size are described by Montgomery (1900) 

 in Feripatus. 



In Anat. Hefte 1902, in dealing with the sperms of man and 

 S. maculosa^ Ivar Broman finds, that is describes, no giant forms, 

 but apparently forerunners of such. 



Other instances may occur hidden away in the literature of sper- 

 matogenesis. The majority of the above cases of twofold spermatozoa 

 rest upon a very firm basis of evidence, and many of them have even 

 been figured. 



Dimorphic forms of eggs have as yet actually been described in 

 only four divisions of the animal kingdom, viz., Rotifera, the aberrant 

 genus Binophilus, Insecta, and Pisces. The instances are: Rydatina 

 senta and various other Rotifera, Dinophilus gyrociliatus (Fig. 6), 

 Phylloxera vastatrix (Fig 7), and coccinea ^), and Raja hatis. To this 

 tangible evidence in support of their existence may be added that 

 afforded by like-twins for the Mammalia (B. S. Schultze), and the 

 important facts yielded by those instances of the production partheno- 

 genetically of young of both sexes. 



With the above testimony, pointing to the existence of two cate- 

 gories of eggs, may be placed that recorded; but, while never yet 

 refuted, universally ignored in the literature of embryology, by von 

 Jhering (in: Biol. Ctrbl., V. 6, p. 532—539, 1886) concerning the 

 invariably like sexes of all the embryos found in one chorion in 

 Praopus hyhridus, an Edentate. 



Among the cases of twofold spermatozoa, already worked out and 

 recorded, there are very few, in which degenerative changes do not 



1) The discovery of the facts in Phylloxera coccinea (quer eus) is 

 àne to Balbiani in 1878 (vide: Observations sur le Phylloxera du chêne, 

 in: Ann. Sc. nat., V. 19, Art. no. 12, p. 8 — 9). This is confirmed by 

 Victor Lemoine (in: Biol. Ctrbl, V. 4, 1884—85, p. 554). Both ob- 

 servers state, that the male-eggs are easily recognised by their lesser 

 size and red-brown colouring, while the female ones are of greater 

 dimensions and of a pale brown tint. The whole of the literature re- 

 lating to Phylloxera vastatrix was not at the writer's disposal. 



