1 8 Cutler, Parthenogenesis in Animals 



equational, so that though four nuclei were formed, there was 

 no reduction of the chromosome number. He also described a 

 fusion of the second polar nucleus with the inner half of the 

 first polar nucleus. The (outer half passed to the periphery and 

 was extruded and fusion with the second and inner- part of the 

 first polar nucleus occurred. 



The result of greatest interest in his investigations was that 

 the chromosomes of the female pronucleus were doubled in 

 number before the first cleavage tjook place. The same pheno>- 

 menon was said tio< occur by Petrunkewitsch ^n the honey bee, 

 and by Delage in the artificial parthenogenesis of sea-urchin 

 eggs. 



Schliep reinvestigated the cytology of the egg of Rhodites 

 rosas. He gives the somatic number of chromosomes as ten or 

 twelve. This number is also found in the oogonia and fhei 

 oocytes, thus confirming the statement that there js noi reduc- 

 tive division. Further, according to this observer, there is no 

 doubling of the chromosome number after maturation has taken 

 place, the cleavage nucleus possessing ten to> twelve chromosomes. 



Tenthredinidm. — The sawflies are very varied as to the 

 manner of reproduction; some (there are which lay partheno- 

 genetic eggs from which only males appear (Nematus ribesii); 

 in other species parthenogenetic eggs are laid from which only 

 females are hatched (Pcecilosoma lutecium); and a third group 

 from which both males and females are produced from partheno- 

 genetic eggs, as in the gallflies. Investigation into the. cyto- 

 logical aspects were undertaken by Doncaster. As the results 

 published for Nematus ribesii are probably incorrect, it is use- 

 less to detail them here. It is hoped that the cytology of the 

 eggs of this insect will be re-examined at somja future date, so 

 that the present discrepancies in the account may "be rectified. 



In Pcecilosoma luteolum and Croesus varus two maturation 

 divisions occur, and the chromosomes do not appear to be re- 

 duced in number. This conclusion is probably correct, but until 

 the spermatogenesis and oogenesis have been studied the point 

 cannot be said to be definitely settled. 



Lepidoptera. — The cases in which parthenogenesis occurs 

 among the Lepidoptera are few. Platner and Henking studied 

 the maturation of the unfertilised eggs of Bombyx mori. Two 

 polar bodies were said to be formed and the chromosomes were 

 thought to be reduced in number. Recently, however, Gold- 

 schmidt found in the Gipsy moth that the oogonia and sperma- 

 togonia of the insects, which had arisen parthenogenetically, 

 contained the normal diploid number of chromosomes. At 

 present our knowledge of the cytology of the unfertilised eggs 

 of the Lepidoptera is very scanty. Qoldschmidt mentions in his 



