GENEOLOGICAL. 391 



showed that three larvae may be reared from a single 

 sea-urchin ovum divided into three pieces, and that 

 a normal blastula might develop from -5^- 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. 



(;') Determination of Sex. 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, Pfliiger, Yung, Maupas, Nussbaum, 

 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 (AnatomiscJie Ergebnisse, Merkel and 

 Bonnet, VIL, 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 



