SEXUAL REPRODUCTION. 



143 



already laid eggs of her neighbours. Meanwhile she is attended 

 by her (frequently much smaller) mate, who deposits milt upon the 

 ova. In the frog, again, the eggs are fertilised externally by the 

 male just as they leave the body of his embraced mate. Or it 

 may be that the sperms are lodged in special packets, which are 

 taken up by the female in most of the newts, surrounded with 

 one of the male arms in many cuttle-fishes, or passed from 

 one of the spider's palps to the female aperture. In the majority 

 of animals, e.g., insects and higher vertebrates, copulation occurs, 

 and the sperms pass from the male directly to the female. 

 Even then the history is very varied. They may pass into 

 special receptacles, as in insects, to be used as occasion demands; 

 or, in higher animals, they may with persistent locomotor energy 

 work their way up the female ducts. There they may soon 

 meet and fertilise ova which have been liberated from the ovary ; 

 or may persist, as we noticed, for a prolonged period ; or may 

 eventually perish. 



Different Forms of Conjugation in Plants. 

 a, zoospores ; b, mould ; c, d, conjugate algas ; e,/, desmid. 



When the sperms have come, in any of these varied ways, 

 into close proximity to the ovum, there is every reason to 

 believe that a strong osmotic attraction is set up between the 

 two kinds of elements. We have often suspected that the 

 approach of the conjugating cells of tw^o Spirogyra filaments 

 (fig. r, d) might be directed along the line of an osmotic current ; 

 and although we must confess that perhaps somewhat rough 

 evaporations, performed a few summers ago, gave no positive 

 confirmation to the idea that glucose or the like might be 



