134 THE EVOLUTION OF SEX. 



matozoa. Through the experiments of Prevost and Dumas (1824), 

 Leuckart (1849), and others, attention was directed to the real import 

 of the sperms, which Kolliker referred to their cellular origin in the 

 testis. The presence of the sperm within the ovum was observed in 

 the rabbit ovum by Martin Barry in 1843; by Warneck, in 1850, for 

 the water-snail, a fact confirmed about ten years afterwards by Bischoff 

 and Meissner; in the frog ovum by Newport (1854); ar »d in successive 

 years it was gradually recognized in a great variety of animals. 



The external devices which secure that the sperm shall reach the 

 ova are very varied. Sometimes it seems more a matter of chance 

 than of device, for the sperms from adjacent males may simply be 

 washed into the female, as in sponges and bivalves, with the nutritive 

 water-currents. In other cases, especially well seen in most fishes, 

 the female deposits her unfertilized ova in the water; the male follows 

 and covers them with spermatozoa. Many may have watched from 

 a bridge the female salmon ploughing along the gravelly river bed 

 depositing her ova, careful to secure a suitable ground, yet not dis- 

 turbing the already laid eggs of her neighbors. Meanwhile she is 

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

 upon the ova. In the frog, again, the eggs are fertilized 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 cuttlefishes, or passed from one of the spider's 

 paips to the female aperture. In the majority of animals — for example, 

 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 fertalize ova which have been liberated 

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

 or may eventually perish. 



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 two 

 Spirogyra filaments (fig. c, d) might be directed along the line of an 

 osmotic current ; and although we must confess that perhaps some- 

 what rough evaporations, performed a few summers ago, gave no 

 positive confirmation to the idea that glucose or the like might be 

 present in appreciable quantity in the water, a recent observer, we are 

 glad to see, claims to have been more fortunate. The spermatozoa, 



