174 HEREDITY AND SEX 



eggs are produced in the same way as are other eggs. 

 They are produced in ovaries that have the same 

 structure as the ovaries that give rise to ordinary 

 eggs. Parthenogenetic eggs differ from spores, not 

 only in their origin in an ovary, but in that they also 

 produce polar bodies like ordinary eggs. Most, but 

 not all, parthenogenetic eggs give rise, however, to 

 only one polar body. Some of them at least fail to 

 pass through the stage of synapsis, and, in consequence, 

 they retain the full number of chromosomes. 



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Fig. 89. — Miastor, sexual male and female (to right). Three larvae 



with young inside (to left) . 



A few examples will bring the main facts before us. 



A fly, miastor, appears in the spring of the year 

 under two forms, male and female (Fig. 89) . The eggs 

 are fertilized and each produces a worm-like larva. 

 This larva produces eggs while still in the larval stage. 

 The eggs develop without fertilization, and produce 

 new larvae, which repeat the process. This method 

 of propagation goes on throughout the rest of the 

 year until finally the adult winged flies reappear. 



The bee is the most remarkable instance, for here 



