Some problems of reproduction. 607 



the formation of tlie segmentation spindle when the male 

 cytoplasm is probably equal in bulk to the female. 



We have noted above that the oosperm in primitive types of 

 syngamy has usually the character of a resting-cell, whereas 

 the fertilised egg of binary sex immediately undergoes brood- 

 division (segmentation). The key to this difference probably 

 lies in the fact just recapitulated. Since the sperm must grow 

 for the conjugation to take place and secrete an enzyme to 

 digest the food granules, the female cytoplasm itself must 

 also grow in presence of this digested f ood^ as is clearly shown 

 in the figures we have referred to. We have seen that such 

 growth at the expense of intra-cellular reserves is the starting- 

 point for brood-division in general. Thus the impulse for 

 division given by the sperm is no essential phenomenon of 

 syngamous union; it is conditioned by the differentiation of 

 binary sex, and is the indirect consequence of that reduction 

 of the sperm which makes its growth within the egg the 

 necessary prelude of complete fusion therewith. 



Bibliography. 



1. Wilson. — ' Atlas of Fertilisation and Karyokinesis,' 1895. 



2. Vejdovsky and Mrazek. — "Umbildung. des Cytoplasma wahreud d. 



Befruchtung. u. Tellteilung.," in 'Arch. mikr. Anat.,' Ixii, 1903. 



Tiie sources of the facts given on Protists are to be found in Lang's 

 'lielirbuch der vergleichenden Auatoinie der Wirbellosen Thiere,' ed. 2, 

 dief. ii, Protozoa, p. , 1901 ; in the Monographs of the Flagellates, Pro- 

 tophytes, and Algae iu Engler an I Prantl's ' Plianzenfamilies,' supplemented by 

 the important papers cited below, each of which has its own bibliography. I 

 must also refer to the storehouse of Wilson's 'The Cell,' ed. 2, 1900, which 

 suffers only from the author's having approached his subject from the 

 Metazoan standpoint. 



Delage, Y. — " Etudes sur la Merogonic," ' Arch. Zool. Exp.,' scr. 3, vol. vii, 



1900. 

 DfiLAGE, Y. — "Sur rintci'pretation do la fccondation merogonique et sur 

 uue theorie nouvelle de la fccondation normalc," ibid (1900). 



