REPRODUCTION AND GROWTH 185 



tion may be reciprocal. Or an animal may alternate between 

 the male and female conditions — only one sex-gland functioning 

 at a certain period. 



Structural {and imperfect) hermaphroditism. Both ovaries and 

 testes may have developed in the same individual but only one 

 or the other may function. Because of imperfect, or unregulated 

 embryonic development the external genital organs may be 

 abnormal so that a true female (carrying an ovary) may simulate 

 a male and vice versa. In such cases (even in man) sex may be 

 indeterminate from external indications. Or there may be " inter- 

 sexes " where individuals recognizable as females may have male 

 organs, and vice versa. 



Plainly the animal organism, in general, is fundamentally both 

 male and female and the condition in which the sexes are placed 

 in separate individuals is a secondary one. 



68. ON PARTHENOGENESIS 

 Parthenogenesis is virgin-reproduction. It occurs in several 

 groups of animals and the condition is either facultative or 

 obligatory : that is, the animals may, for a time, reproduce 

 sexually and then, for a time, parthenogenetically (facultative). 

 Or the only method of reproduction that is known may be par- 

 thenogenesis (obligatory). We must regard the animal so re- 

 producing as a female, for its germ-cells have all the appearance 

 of ova. They are simply emitted, or laid, by the parent and they 

 develop without being " activated " by a spermatozoon, or in 

 any other w^ay that is apparent (see below). In the obligatory, 

 parthenogenetic animals we may speak of all the individuals as 

 females, in respect of the appearances and modes of origin of 

 the germ-cells. There are no males. There may be said to 

 be '' sex " but not in the sense of our former definition of 

 the term — which definition includes the appearance of two 

 kinds of germ-cells, a particular mode of " activation " of the 

 ovarian cell by the testicular one and the consequent processes 

 of amphimixis. 



68«. Artificial Parthenogenesis. Finally it is to be noted 

 that there are animals which are typically differentiated into males 

 and females but in which the female gametes, or ova, may be 

 made to segment and develop without being fertilized, in the usual 



