52 SCIENCE PROGRESS 



drone to a female. The same conclusion is reached from the 

 study of all kinds of parthenogenetic animals. It is conceivable, 

 where a creature contains the determinants of both sexes, as 

 appears to be the case in most animals produced from fertilised 

 eggs, that circumstances may determine which sex dominates, 

 but there is no real evidence for this, and many things make 

 it improbable. 



Parthenogenesis might be expected to help in answering 

 the question "What is the function of sex?" but the result 

 of such inquiry is disappointing. Some sort of sexual process 

 is so widely distributed that it is often assumed to be universal. 

 Yet several species of animals, both Insects and Crustacea, are 

 known in which no male has ever been found, and which can 

 live and reproduce to all appearance indefinitely without the 

 occurrence of conjugation. It is true that these things have 

 been studied for only a short time and by few observers, and 

 that where males were once thought to be absent they have 

 since been discovered, but when twelve thousand individuals 

 of a species are reared and no male discovered among them, 

 as has been done with Cynips kollari, 1 one may assume that 

 bisexual reproduction must at least be so rare in the species 

 as to be practically negligible. And yet the purely partheno- 

 genetic species seem to persist and flourish not less vigorously 

 than those which conjugate with unfailing regularity. The 

 physiological basis of sex is still a mystery. 



1 Alternating Generations, Adler and Straton, Oxford, 1894, p. 165. 



