SAWFLIES 5 I 7 



itself certain evidence of the occurrence of parthenogenesis, hut 

 this has heen placed heyond doubt by taking females bred in con- 

 finement, obtaining unfertilised eggs from them, and rearing the 

 larvae produced from the eggs. This has been done by numerous 

 observers with curious results. In many cases the partheno- 

 genetic progeny, or a portion of it, dies without attaining full 

 maturity. This may or may not be due to constitutional weak- 

 ness arising from the parthenogenetic state. Cameron, who has 

 made extensive observations on this subject, thinks that the 

 parthenogenesis does involve constitutional weakness, fewer of 

 the parthenogenetic young reaching maturity. This he suggests 

 may be compensated for — when the parthenogenetic progeny is 

 all of the female sex — by the fact that all those that grow up 

 are producers of eggs. In many cases the parthenogenetic young 

 of Tenthredinidae are of the male sex, and sometimes the abnormal 

 progeny is of both sexes. In the case of one species — the com- 

 mon currant sawfly, Nematus ribesii — the parthenogenetic progeny 

 is nearly, but not quite, always, entirely of the male sex ; this 

 has been ascertained again and again, and it is impossible in 

 these cases to suggest any advantage to the species to compensate 

 for constitutional parthenogenetic weakness. On the whole, it 

 appears most probable that the parthenogenesis, and the special 

 sex produced by it, whether male or female, are due to physio- 

 logical conditions of which we know little, and that the species 

 continue in spite of the parthenogenesis, rather than profit by it. 

 It is worthy of remark that one of the species in which partheno- 

 genesis with production of males occurs — Nematus ribesii — is 

 perhaps the most abundant of sawflies. 



Although many kinds of Insects display the greatest solicitude 

 and ingenuity in providing proper receptacles for their eggs, and 

 in storing food for the young that will be produced, there are 

 extremely few that display any further interest in their descend- 

 ants ; probably, indeed, the majority of Insects die before the 

 eggs are hatched, one generation never seeing the individuals of 

 another. It is therefore interesting to find that a fairly well 

 authenticated case of maternal attachment, such as we have 

 previously alluded to as occurring in earwigs, has been recorded 

 in Perga lewisii, an Australian sawfly of the sub-family Cim- 

 bicides. The mother, having deposited about eighty eggs on 

 the leaf of a Eucalyptus, remains with them until they hatch, 



