yo Annals Entomological Society of America [Vol. Ill, 



life with human blood diet show that female fleas of all species 

 outlive the male by several weeks. This is doubtless true also 

 under natural conditions, where we find in collecting fleas from 

 the host that the females predominate markedly. 



The eggs rccjuire ojjtimum conditions of temperature and mois- 

 ture for hatching. They have never been found on the host 

 €xcept in one instance. In this case a dog was used in the 

 laboratory for supplying fresh fleas ; this was done by placing the 

 canine on sheets of paper which in a few hours were littered with 

 ii large number of flea eggs. These were laid loosely on the host 

 b\- the fleas, the eggs falling to the paper, where they were 

 collected. Flea eggs have never been found on man. and if 

 present, would not hatch under normal conditions of the body 

 temperature. We have found that keeping eggs in the incubator 

 at blood heat is sufticient to prevent hatching. If the eggs were 

 laid on the host we would certainly expect to find them on the 

 squirrel, on which animal fleas are most abundant. We ha\-c 

 taken from two squirrels, respectively, 225 C. aciitiis and 376 of 

 the same species; but in no instance even where fleas are present 

 in such large numbers ha\'e we been able to find eggs even after 

 carefully combing the host. The C. acutiis is by all means the 

 best criterion in this matter, since we have found that it lays 

 more eggs than any other of the rodent fleas. 



The eggs are laid singly in small clusters, and may be viscous 

 as in P. irritans, C. fasciatus, L. cheopis, C. aciitus; or dry as in 

 C. canis and C. musculi. The former adhere to the medium in 

 which they are laid, and the eggs of the last two species are laid 

 loosely, so that they roll when shaken in the vial containing them. 



Eggs may be laid while the insect is still under the influence 

 of an anaesthetic ; when covered by a glass slip ; and when exposed 

 to strong sun light. 



It appears to be the lirst impulse for the female lo lay its 

 eggs when removed from the host and placed under artificial 

 conditions. The great majority of the eggs obtained were laid on 

 the first day, beginning almost immediately after the fleas were 

 captured. It is a common observation that many females with 

 their abdomens distended lay their eggs as soon as tlie vial is 

 closed over them. The number of eggs laid at one laying by 

 diftcrent s]x^cies. \aries from 3 to 18; the rat fleas a\-eraging 6 

 and the squirrel fleas lay as many as 18. 



