GENEOLOGICAL. 391 



showed that three larva may be reared from a single 

 sea-urchin ovum divided into three pieces, and that 

 a normal blastula might develop from -g^ of an 

 ovum. To this development of fragments he ap- 

 plied the term merogony. 



It will be observed that while Loeb showed. that 

 normal development was possible without the pa- 

 ternal nucleus, Delage showed that this was possible 

 without the maternal nucleus. If both sets of ex- 

 periments are duly confirmed, there will be need for 

 some reconstruction in the current views as to fer- 

 tilisation. 



(j) Determination of 8 ex. — A reference should 

 be made here to the numerous experiments on the 

 factors which determine whether a germ is to be- 

 come a male or a female organism. The investi- 

 gations of Born, Pfluger, Yung, Maupas, Kussbaum, 

 and Diising are of especial importance ; but we may 

 refer for detailed discussion to The Evolution of 

 Sex (4th edition, revision) by Prof. Patrick Geddes 

 and the writer, and to the dispassionate review by 

 Henneberg {Anatomisclie Ergehnisse, Markel and 

 Bonnet, VII., 1897; pp. 697-721). We must be 

 content with a general summary : — 



The epoch at which the sex is finally determined 

 is variable in different animals, and diverse factors 

 operative at successive epochs. Theological and meta- 

 physical theories of sex have preceded the sci- 

 entific ; observation and statistics have been resorted 

 to before experiment; and over 500 theories in all 

 have been set forth. That there are two kinds of 

 ova is still for the most part an assumption ; that 

 the entrance of more than one spermatozoon fre- 

 quently occurs, and is a determining factor, is 

 erroneous. Thury's emphasis on the age of the ovum 



