1 Introduction 1

2 Cytological characteristics of the Cecidomyiidae 8

2.1 Elimination divisions and formation of primordial germ cells 8
2.1.1 Morphology 9
2.1.1.1 Time of chromosome elimination and segregation of the
germ-line nucleus 11
2.1.1.2 Incomplete elimination 12
2.1.1.3 Mitotic gradient 13
2.1.1.4 A gradient of chromosome elimination 14
2.1.1.5 Types of chromosome elimination 16
2.1.1.6 The fate of eliminated chromosomes 22
2.1.1.7 Heteropycnosis in the germ-line nuclei 23
2.1.2 Experimental analysis 25
2.1.2.1 Experiments involving cauterisation 25
2.1.2.2 Experiments with ultraviolet irradiation 25
2.1.2.3 Experiments involving constriction of eggs 26
2 1.2.4 Experiments with centrifugation 27

2.2 Fate of female primordial germ cells, organisation of egg follicle,
and the origin of oosome material 35

2.3 Spermatogenesis 41

3 Life cycles and chromosome cycles of Cecidomyiidae 53

3.1 Lestremiinae 54
3.1.1 Tekomyia populi Mohn 54
3.1.1.1 Thelytokous paedogenesis 54
3.1.1.2 Arrhentokous pacdogenesis S S
3.1.2 Mycotbila nikoleii Mohn 56
3.1.2.1 Thelytokous pacdogenesis 57
3.1.2.2 Metamorphosis and bisexual generation 57
3.1.3 Mycotbila barnesi Edwards 57
3.1.4 Mycophilaspeyeri Barnes 57
3.1.4.1 Thelytokous paedogenesis 58
3.1.4.2 Arrhenotokous and amphitokous pacdogenesis 59
3.1.4.3 Metamorphosis and bisexual reproduction 59
3.1.4.4 Cytology of paedogenesis 60
3.1.4.4.1 Cytology of the female embryos 60
3.1.4.4.2 Cytology of the male embryos 62
3.1.4.5 Cytology of bisexual reproduction 64

3.2 Porricondylinae 64
3.2.1 Henria psalliotue Wyatt 64
3.2.2 Leptosyna nervosa (Winnertz) 65
3.2.3 Heteropezala tenuis Wyatt 65
3.2.4 Heteropeza pygmaea Winnertz ( -Oligarces paradoxes Meinert) 66
3.2.4.1 Thelytokous pacdogenesis 67
3.2.4.2 Arrhenotokous and amphitokous pacdogenesis 70
3.2.4.3 Bisexual reproduction and imaginal parthenogenesis 72
3.2.4.4 Cytology of pacdogenesis 75
3.2.4.4.1 Cytology of the female embryos 75
3.2.4.4.2 Cytology of the male embryos 77
3.2.4.5 Cytology of bisexual reproduction and imaginal
arthenogenesis 81
3.2.4.6 Sex determination and the problem of a somatic
haplo-diploidy 83
3.2.5 Brittenia fraxinicola Edwards 85
3.2.6 Miastor metraloas Meinert 85
3.2.6.1 Thelytokous paedogenesis 86
3.2.6.2 Arrhenotokous and amphitokous pacdogenesis 87
3.2.6.3 Metamorphosis and bisexual reproduction 88
3.2.6.4 Cytology of paedogenesis 88
3.2.6.4.1 Cytology of the female embryos 88
3.2.6.4.2 Cytology of the male embryos 89
3.2.6.4 Cytology of bisexual reproduction 90
3.2.7 Miastor castaneae Wyatt 91

2.3 Cecidomyiinae 91
3.3.1 Oogenesis 91
3.3.1.1 Small nuclei 91
3.3.1.2 Behaviour of the S-chromosomes 92
3.3.1.3 Behaviour of the E-chromosomes 93
3.3.1.4 Meiotic divisions 99
3.3.2 Sex determination and sex ratio 105

4 The relationship between S-chromosomes and E-chromosomes 108

5 The role of the E-chromosomes 114

6 The polytene chromosomes 117

References 127
Acknowledgements 137
Species Index 139