PHYSIOLOGY OF SEX AND REPRODUCTION. 227 



Antcdon. Yet more in plants is the liberation of male elements, 

 and notably that of pollen-grains, a passive dehiscence, and fertiliza- 

 tion a matter of chance, only reduced by the prodigal wealth of 

 material. Secure as the methods of fertilization of flowers by the 

 aid of insects often are, the margin of risk is wide: and this is yet 

 more marked when the pollen is carried by the wind. It is true that, 

 both in plants and animals, there are subtle attractions between the 

 essential elements, but this is only at a close range; and the external 

 union is in many cases none the less random. 



It must be allowed that the primary importance of the timely 

 encounter of the ovum and spermatozoon has perpetuated in the 

 various groups a varied series of adaptations securing fecundation. 

 At the same time, the increasing differentiation of the sexes has in 

 the higher animals been enhanced by psychial as well as physical 

 attractions, thus more and more insuring the continuance of the 

 species. 



Fig. 86. — Male of Paper Nautilus (A rgonauta) , with its 

 modified arm. — From Leunis. 



A not unfrequent mode of fecundation is by means of spermato- 

 phores, or packets of spermatozoa. These may be seen at times 

 attached to the earthworm, or found within the leech and snail. Even 

 in newts spermatophores are formed, which are taken up by the 

 females. 



In the spider the spermatoza are stored in a special receptacle on 

 the palp, and hence hastily transferred to the fierce female. In cuttle- 

 fishes this mode of impregnation is yet more marked. One of the 

 ' ' arms ' ' of the male, much modified and laden with spermatophores, 

 is thrust, or in many cases bodily discharged into the branchial cavity 

 of the female, where it bursts. Such a discharged arm was, on first 

 discovery, regarded as a parasite, and hence received the name ol 

 Hedocotylus. A curious aberration from the ordinary relations is. 



