PART II. EMBRYOLOGY OF INSECTS 



a. The egg 



INSECTS as a rule arise from eggs which are laid in a great 

 variety of situations, those species which are viviparous being 

 exceedingly few in number compared with the class as a whole. It 

 is noteworthy that Ley dig has- found in the same Aphis, and even in 

 the same ovary, an 

 egg-tube producing 

 eggs, while a neigh- 

 boring tube was pro- 

 ducing viviparous 

 individuals. 1 The 

 viviparous species are 

 confined to certain 

 May-flies, the Aphi- 

 dae, Diptera (Sar- 

 cophaga, Tachinidae, 

 CEstridae, and Pupi- 

 para), and to certain 



(Stylo- Fro. 482. Female Dyticus. laying eggs : A, ovipositor ex- 



, tended. , egg of Notonecta, attached to stem of rush. C, egg 



piaae and SOme Ota- of Dyticus, laid in excavation in rush. After Kegiuibart, from 



,,..-, N Muill'. 



phylmidae). 



The number of eggs laid varies from a very few, as in the Collem- 

 bola and in the Psocidae, or 15 or even less in certain fossorial wasps, 

 and from 20 to 35 in some locusts to many thousands in the social 

 insects, the honey-bee laying by estimate over 1,000,000 eggs in the 

 course of her life. Dr. Sharp thinks that from 50 to 100 may perhaps 

 be taken as an average number for one female to produce. The eggs 

 of insects with a complete metamorphosis are said by Brauer to be 

 smaller in proportion to the parent than those laid by ametabolous 

 or heterometabolous insects. In this respect the insects are par- 

 alleled by the birds, the highest forms laying smaller eggs than the 

 water birds, ostrich, Apteryx, etc. 



1 Acta Acad. German., xxxiii, 1867, No. 2, p. 81. Quoted by Dr. Sharp, Insecta, 

 p. 14-'. 



515 



