HISTORY OF INSECTS. 279 



Sixteen ova, one from each ovarian tube, are usually 

 enclosed within each egg-capsule. The latter is formed from 

 the secretion of the colleterial glands. Each egg is enclosed 

 in an oval shell, on which there are several little holes 

 (^micropyles), through one of which a spermatozoon enters. 

 Spermatozoa, from the female's store within the spermatheca, 

 are included in the egg-capsule. The development may be 

 inferred from what has been said in regard to that of Insects 

 in general, and it has already been mentioned that there is 

 no metamorphosis. 



History. — Insects must have appeared comparatively early, 

 for remains of a cockroach-like form have been found even 

 in Silurian strata. The higher forms with complete meta- 

 morphosis appear much later {e.g., beetles in the Carboni- 

 ferous), but it is likely that the Palaeozoic Insects were 

 mostly generalised types, prophetic of, rather than referable 

 to our modern orders. 



As to the pedigree of Insects, the wingless CoUembola and 

 Thysanura are doubtless primitive. They lead us back to 

 some of the less specialised Myriopods (e.g., Scolnpendrelld), 

 back further to Peripatus, which links the Tracheate to the 

 Annelid series. But though the wingless primitive Insects, 

 the simple types of Myriopod, and Peripatus, may represent 

 ascending grades of evolution ; what the precise path has 

 been we do not kno^v, nor are we much wiser about the 

 relationships among the different orders of Insects. 



