REPRODUCTION AND HEREDITY 141 



unfertilised eggs that may be produced in the rudimentary 

 ovaries of workers, and this might be explained by a sup- 

 pression of the reduction division in maturation. R. Gold- 

 schmidt (1923), in a discussion of such alleged exceptional 

 modes of reproductive behaviour, calls attention to the 

 possibility of non-disjunction (p. 130) in maturation as the 

 cause. " If such an abnormality occurs among the 

 Hymenoptera, it would be possible for ripe eggs to be 

 produced containing two ^-chromosomes as well as ripe 

 eggs with none. The first would give females partheno- 

 genetically whilst the latter would, after fertilisation, give 

 males." 



Thus far we have considered the germ-cells and the 

 hereditary factors borne, as we believe, in their chromosomes; 

 these must be regarded as the essential elements in repro- 

 duction. They require, however, for their action, many 

 accessory structures and processes which, in the pairing 

 and breeding of insects, are often conspicuous, characteristic, 

 and noteworthy. The eggs of a female insect are developed 

 in her ovaries (Fig. 34) — a pair of organs each consisting of a 

 number of tubes to which the contained eggs as they ripen 

 give a '* beaded " aspect. Each egg needs to accumulate 

 a store of food-material (yolk) for the nourishment of the 

 embryo which, it may be hoped, will grow from it ; this food- 

 stuff is in many insects obtained at the expense of other cells 

 in the ovarian tube, '' nurse- cells " as they are called, which 

 lie in groups between successive eggs, or form a single 

 group at the fine terminal end of the tube, the eggs keeping 

 contact with them by means of protoplasmic threads. 

 Where there are no nurse-cells the " follicular cells," which 

 form a sheet or follicle closely enveloping each egg, supply 

 food material, and each foUicle secretes on its inner surface 

 the shell of the egg. This is a relatively hard protective 

 envelope of characteristic shape in various families of 

 insects — globular (Plate V,? B), cylindrical, elongate, and 

 rounded at either end (Plate VI, A), flat and disc-Hke — often 

 adorned with sculptured markings which may indicate the 



