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OBSERVATIONS ON THE LARVAE OF FLEAS. 
By A. W. BACOT, 
Entomologist at the Lister Institute of Preventive Medicine, 
and W. G. RIDEWOOD, 
Lecturer on Biology at the Medical School of St Mary's Hospital, London. 
(With 6 Text-figures.) 
Introductory Remarks. 
Fleas are insects that undergo a complete metamorphosis in the 
course of their development from egg to adult. The eggs laid by the 
mother are not, as are the eggs of lice, attached in any way to the skin, 
fur or feathers of the animal on which the parents are parasitic. They 
fall into the nest, or drop to the ground within the lair or “ run ” of the 
host. Hatching takes from three to ten days according to the tem¬ 
perature 1 . The larvae are active, whitish maggots, eyeless and legless, 
which are not parasitic, but feed on organic matter in the host’s bed, 
or in the dust that collects on the ground in its proximity. 
The larva, after undergoing two moults, spins a cocoon, within 
which it pupates, passing through a longer or shorter quiescent phase, 
and gradually assuming the adult form. When the perfect insect finally 
emerges from the cocoon it takes the first opportunity of lodging itself 
in the fur or feathers of some new host, exhibiting a preference for 
individuals of the same species as that upon which the parents were 
parasitic. 
1 For recent observations on the influence of temperature and humidity upon hatching 
of eggs see Journal of Hygiene , vra. 2, May 1908, Plague Report xxix. p. 244 ; ibid. xi. 
Plague Supplement ii. Report lv. Jan. 1913, pp. 304-313 ; and A. W. Bacot. ibid. Plague 
Supplement in. Report lxix. Jan. 1914, pp. 482-499, 641-643, 645 
