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TEXT-BOOK OF ENTOMOLOGY 



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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 

 & place." In Chrysopa eggs the micro- 



/ /-? 1 Pyl e forms a conspicuous button- 



e " - 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- 

 mann Keimhautblastem (K) 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 (Proctotrypidee) 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. 



Fifi. 51)2. Diagrammatic median section 

 throusfh eg* of Musca in sta^i- of fertilization 

 (Incorporating the figures of Henking and 

 Klochmann) : <//., chorion ; </, dorsal ; , ven- 

 tral side of the cfrsr ; <lli, yolk-membrane; do, 

 nutritive yolk ; (/, gelatinous cap over the 

 mitTopylc (in); A', outer layer of plasma 

 (Keimhautblastem) ; /. male and female pro- 

 nucleus liefore copulation ; /', directive body 

 (Eichtungskorper). After Korschelt and 

 lleider. 



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, Mrlne angusticnllis produces a large number of very small eggs, 

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



