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TEXT-BOOK OF ENTOMOLOGY 



Another use of the micropylar apparatus noticed by Ayers in the 

 egg of the tree-cricket is that it " serves as a thick, roughened plate, 

 against which the insect may push when ovipositing, without injury 

 to the egg, and without danger that the ovipositor slips from its 

 g place." In Chrysopa eggs the micro- 



pyle forms a conspicuous button- 

 like knob, resembling the finely 

 milled head of a certain kind of 

 screw. 



Internal structure of the egg. 

 The egg-contents are surrounded by 

 an outer layer of protoplasm or 

 formative yolk, which is separate 

 from the inner parts of the egg 

 (Fig. 502, do), the latter being 

 mostly composed of the nutritive 

 yolk-element. The superficial pro- 

 toplasmic layer, called by Weis- 

 manii Keimhautblastem (TiT) is, in 

 a few cases, afterwards entirely 

 lost, but in most instances forms a 

 very thin layer of clear protoplasm, 

 slight in extent compared with the 

 yolk-mass within. 



The eggs of insects are rich in 

 yolk, only certain eggs, such as those 

 of the Aphides and the egg para- 

 sites (Proctotrypidae) being poor in 

 yolk. The eggs of heterometab- 

 olous insects have been said by 

 Brauer to contain relatively more 

 yolk than those of the Metabola, 

 particularly the Diptera; though, 

 as Wheeler observes, this rule has 

 some exceptions, the eggs of the 

 17-year Cicada being very numerous 

 and small. 



This he thinks is a greater advantage to the insect than the production of a 

 few large eggs, " when we consider the extremely long period of larval life and 

 the vicissitudes to which the larvae may be subjected during all this time." 

 "Similarly, Meloe angusticollis produces a large number of very small 

 while the eggs of the smaller beetles (Doryphora, e.g.) are much larger. But 



(Keimhautblastem) ; p, male and female pro- 

 nucleus before copulation ; r, directive body 

 (Richtungskiirper). After Korschelt and 



VTjUJlAH 



