24 Hewitt, Cytological Aspect of PartJienogenesis in Insects. 



(lOl), MorfTan (67), and Seeliger (83), and more recently 

 by Delafje (28, 29, 30), their observations flatly contradicted 

 those of Boveri. The Plutei which they obtained by 

 fertilising enucleated portions of eggs with spermatozoa of 

 a different species, did not bear wholly paternal characters, 

 but maternal ones also. They found that the nuclei vary in 

 size ; the nucleus is often below the normal size in embryos, 

 having small cells coming from nucleated portions of 

 ova, consequently it is not at all certain that the nuclei 

 were absent in the fragments which gave rise to Boveri's 

 plutei. Further, the hybrid plutei which develop from 

 whole fertilised ova are very variable, their characters are 

 not necessarily intermediate between those of the parent 

 species ; some may be intermediate, but there are others 

 having characters wholly paternal. 



These observers performed their experiments much 

 more carefully than Boveri, who did his very roughly, 

 and did not demonstrate the absence or presence of the 

 nuclei in the fragments. Nor did he obtain his enucleated 

 portions of ova, if there were any [there is no proof that 

 there were], by cutting them up individually. The results 

 of Delage and others are much more trustworthy. But 

 in spite of the fact that Boveri's experiments have been 

 contradicted, though he has attempted to defend his views 

 (16), a great amount of faith is placed in them. The 

 tendency is to take it as a proven fact, and to argue on 

 the assumption, that the chromosomes are the sole bearers 

 of hereditary characters, which I believe to be far from 

 proven. 



Working on this assumption. Castle (21), Sutton (92), 

 Hacker (42), Montgomery (65), and others have sug- 

 gested hypotheses to account for and explain the nature 

 of heredity and sex. Each worker has attempted to 

 make the chromosome data fit in with the theory which 



