362 THE GERM- PLASM 



of the hermaphrodites is due. Siebold attempted to explain 

 this difficulty by supposing that the eggs which produced 

 hermaphrodites were imperfectly fertilised. He found that in 

 the queen, after producing hermaphrodites, the receptaclum 

 was almost empty : and as drones arise from unfertilised, and 

 females from fertilised eggs, the view that imperfect fertilisa- 

 tion must produce hermaphrodites appeared to be a plausible 

 one. It was not known at tliat time that a single spermatozoon 

 suffices for fertilisation, and at the present day we are no longer 

 justified in using such an expression as 'imperfect fertilisation." 

 Whenever a living spermatozoon enters an egg, the latter 

 becomes fertilised ; and an imperfect fertihsation could onlv be 

 supposed to occur if the spermatozoon is abnormal — if, for 

 instance, it contains too few idants. But even if such a case 

 occurred, it would be of very little value theoretically, and we 

 could only state that the determination of sex did not take place 

 in all the double determinants at once, but only in certain larger 

 or smaller groups, — in the case of the germ-cells as well as of the 

 dimorphic parts of the body. Besides the ordinary case, in 

 which the sexual gland of an individual was developed on the 

 female type on the right side and the male type on the left, 

 other instances occurred in which female and male germ-follicles 

 were formed on the same side, seminal tubules and ovarioles 

 being present close together. With reference to this fact, von 

 Siebold remarks that •• the hermaphroditism of the sexual appa- 

 ratus hardly ever corresponded to that observable in the external 

 form ; " and this seems to me to be of special theoretical interest, 

 as it allows us to conclude with certainty that the harvtony 

 of the noniial condition is due to a sinuiltaneoiis decision 

 respecting the double determinants of the germ-cells and those 

 of the body, and not to a primary determination of sex in the 

 sexual glands, from which tlie somatic male or female sexual 

 characters would only be determined secondarily. The existence 

 of double determinants in the germ-plasm can be actually proved 

 in the case of bees. For if any egg can develop into a male 

 or female according to whether it is fertilised or not, it must 

 contain both kinds of determinants. 



Although this assumption is undoubtedly a correct one, it 

 alone is insufficient, because the secondary differences of sex 

 do not always only concern single cells or groups of cells which 

 correspond exactly in the two sexes, such as, for example, the 



