cxlviii On the Affinities of the Pulicites. 



" It has been discovered," says Baker, "by putting the eggs of fleas 

 into a small glass tube, and keeping it constantly warm in one's bo- 

 som, that in the midst of summer, they hatch in four days : then feed- 

 ing the maggots with dead flies, which they suck greedily, in eleven 

 days they come to full perfection of their reptile state." This experi- 

 ment, which, however, is not original, I cannot boast of having con- 

 firmed, but it seems far from improbable that it is strictly and literally 

 true. After all, it is not perhaps a matter of vital importance on what 

 the maggot feeds, seeing that its figure and metamorphosis are esta- 

 blished beyond all question. 



When full grown, the larva seeks out some crack or other safe place 

 of concealment, and there, after remaining some time in a motionless 

 state, spins itself a delicate cocoon of the softest and most slender 

 silk : the interior of this cocoon is of the purest white, but the exte- 

 rior is rougher and soiled with dust, and within this it changes to a 

 pupa, which at first is of a milk white, but gradually changes colour, 

 and finally assumes that of the imago. The pupa clearly exhibits the 

 form of the future imago, the legs being distinctly visible, and all their 

 articulations readily traceable ; they are partially adherent to the bo- 

 dy laterally, but are severally inclosed in a distinct case or skin : the 

 pupa emerges from the anterior extremity of the larva, the pellicle 

 of which, by the wriggling motion of the creature, is gradually pushed 

 backwards, and finally adheres in a crumpled form to the posterior 

 extremity. The pupa has thirteen segments, including the head ; the 

 terminal segment or telum is extremely small. There is a striking 

 discrepancy in the accounts given by authors of the time occupied in 

 the different states of larva and imago : thus we find some asserting 

 that the state of egg lasts four days, that of larva seventeen days, that 

 of pupa four days, and that the imago lays eggs in three days more ; 

 so that a calendar month suffices for the entire round of its existence, 

 and a year for twelve such rounds. Others again describe the period 

 as much more protracted, and make the round of existence occupy 

 nearly a year. There is no reason for doubting the assertions of 

 any of these observers, but the conclusions they deduce are not al- 

 ways equally unexceptionable. I have no hesitation in expressing 

 my belief that the periods vary with the season, the temperature, and 

 also with the species ; and that no positive conclusions are to be 

 drawn, until our observations are infinitely multiplied, and are record- 

 ed with greater precision. 



The final change takes place within the cocoon, and the flea then 

 perforates his silken dormitory and enters on his jumping career, in 



