In Hemiptera only eleven and in Collembola only yolk, and that the mesenteric epithelium becomes reinforced by six abdominal segments have been detected.
No indications beyond those furnished by comparative anatomy help us to unravel the phylogeny of the Collembola.
Lubbock (Lord Avebury) separated the springtails as a distinct order, the Collembola, and by many students this separation has been maintained.
It is better, on the whole, to regard the Thysanura and Collembola as sub-orders of a single order, the Aptera.
In most Collembola the spring appears to belong to the fifth abdominal somite, but Willem, by study of the muscles, has shown that it really belongs to the fourth.
