The union of the. two sexual elements seems to make a broad distinetion 
between sexual and asexual reproduction. But the well-ascertained cases 
of Parthenogenesis prove that the distinction is not really so great as it at 
first appears; for ovules occasionally, and even in some cases frequently, 
become developed into perfect beings, without the coneourse of the male 
element. 
Ca. Darwın: The Variation of Animals and Plants under 
Domestication. London 1868. Vol. II. pag. 359. 
In other Orders, from unknown causes, but apparently in some in- 
stances owing to parthenogenesis, the males of certain species have never 
been discovered or are excessively rare, as with several of.the Cynipidae. 
CH. Darwın: The Descent of Man and Selection in Re- 
lation to Sex. London 1871. Vol. I. pay. 314. 
