In Hemiptera only eleven and in Collembola only yolk, and that the mesenteric epithelium becomes reinforced by six abdominal segments have been detected.
Collembola (Spring-tails): with six abdominal segments; appendages of the first forming an adherent ventral tube, those of the third a minute " catch," those of the fourth (fused basally) a " spring."
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.
- The Aptera are divided into two divergent sub-orders, theThysanura or bristle-tails, and the Collembola or springtails.
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.
Lubbock (Lord Avebury), "Monograph of the Collembola and Thysanura," Ray Society, 1873.
Oudemans, Bijdrage tot de Kennis den Thysanura en Collembola (Amsterdam, 1888); B: Grassi, who published between 1885 and 1889 a series of memoirs entitled "I progenitori dei Miriapodi e degli Insetti," in the Atti Accad.
In addition to this work of Willem, valuable anatomical papers on Collembola have been published by H.
Absolon has also written on the Collembola of caves.
Schott, C. Schaffer and others, have published many systematic papers on Collembola, as has F.