SEX IN LIVING FOKMS " 99 



of each forefoot, which occurs at this period. At the 

 end of the breeding season, these temporary thumbs, 

 being no longer needed, disappear. 



In some species in which internal impregnation 

 occurs, there is no contact between the species, but by 

 some means not yet understood, the spermatozoa dis- 

 charged by the male find their way into the internal 

 passages of the female, where the ovules are impreg- 

 nated. 



In serpents, fecundation occurs by mere contact of 

 the sexual organs. In snails, which have already been 

 mentioned as hermaphrodite animals, each individual 

 possessing in a perfectly developed state both male 

 and female organs, internal fecundation occurs after 

 a very curious fashion, thus described by the eminent 

 naturalist, Prof. T. R. Jones, F. R. S., of London: 



''The manner in which they copulate is not a little 

 curious, their union being accompanied by preparatory 

 blandishments of a very extraordinary kind, that to a 

 sjDectator would seem rather like a combat between 

 mortal foes than the tender advances of two lovers. 

 After sundry caresses between the two parties, dur- 

 ing which they exhibit an animation quite foreign to 

 them at other times, one of the snails unfolds from the 

 right side of its neck, where the generative orifice is 

 situated, a wide sacculus, which, by becoming everted, 

 displays a sharp, dagger-like spiculum, or dart, at- 

 tached to its walls. Having bared this singular 

 weapon, it endeavors, if possible, to strike it into some 

 exposed part of the body of its paramour, who, on the 

 other hand, uses every precaution to avoid the blow, 

 by speedily retreating into its shell. But, at length, 

 having received the love-inspiring wound, the smitten 

 snail prepares to retaliate, and in turn uses every 



