INHERITANCE IN PARTHENOGENESIS 57 



8. Inheritance in Cases of Parthenogenesis 



It would be interesting to know with precision what the facts 

 of inheritance are in cases where development proceeds from 

 an unfertilised ovum, particularly in those cases where the 

 parthenogenesis continues uninterruptedly for many generations. 

 On general grounds, from the absence of fertilisation, one would 

 expect to find few new departures or progressive variations ; 

 but rather, on the other hand, hints of degeneracy. The ob- 

 served facts are still very few. 



Experiments which Prof. Weismann (1893, p. 344) made on 

 a small crustacean (Cypris reptans) showed a very high degree 

 of uniformity between parent and offspring, with occasional 

 exceptions, which he regarded as exhibiting reversions to an 

 ancestral form many generations removed. 



Dr. Warren's (1899) measurements of successive partheno- 

 genetic generations of Daphnia magna also gave evidence of 

 slight variability (i.e. of incompleteness of hereditary resem- 

 blance). They seemed to favour the view that "inheritance 

 in parthenogenetic generations resembles that from mid-grand- 

 parent to grandchildren." 



9. Wherein the Physical Basis precisely consists 



The fertilised egg-cell divides into many cells ; these arrange 

 themselves in various ways ; they grow and multiply ; they 

 exhibit division of labour and the structural side of this which 

 we call differentiation ; they form tissues and organs ; they 

 become integrated into a body ; they reproduce the likeness of 

 the parental type with variations. Meanwhile, some of the 

 cells remain apart from body-making or differentiation, and 

 form the beginnings of the reproductive organs, whence their 

 descendants the mature germ-cells are by-and-bye liberated 

 to start another generation. That this next generation is also 

 after the parental type is due to the continuous lineage of cells 



