1 9 1 o] California Rodent Fleas 7 1 



THE PROCESS OF HATCHING. 



C . aciitiis. 



Six eggs laid while the females were kept under observation 

 were examined from time to time until hatched seven to nine 

 days later. One egg, was observed microscopically during the 

 entire process ; the other fi\-e eggs used as controls were examined 

 occasionally. 



On the seventh day of incubation at room temperature the 

 premonitory signs of hatching were discerned in a very faint rising 

 and falling of the exochorion (outer shell layer) on one side of the 

 shell. During the night, seven hours later, the movement grew 

 more extensive, the pulsations becoming quite pronounced, caus- 

 ing the Qgg to shift slightly from its position. On the morning 

 of the eighth day a deep gash was observed in the side of the egg. 

 The gash is made by the egg opener, a wedge-shaped, horny, claw- 

 like structure on the dorsal side back of the 'head of the embryo. 

 This is operated so as to hew through the resistant shell by a 

 series of slits or gashes. The initial gash increases slowly in 

 length, encircling the egg within an hour. 



In the course of a few hours, seven successive gashes are 

 made, the location of these is quite constant; two on each side 

 of the egg and three at the center, the middle of the latter 

 being the most distinct. The young worm produces these slits 

 through the chorion (inner skin of shell) by turning with its 

 dorsal side against the shell, striking with the egg pick first 

 against the base of the egg, rising on its hind prolegs and striking 

 rapidly as it climbs upwards. Prior to each stroke the egg pick 

 is poised deliberately, the weight of the head accelerating the 

 blow ; this is augmented occasionally by a lateral shaking of the 

 head. 



When the last slit encircles the shell, the embryo is at the 

 most active stage, it effects a complete rotation in its shell at 

 intervals of ten minutes. The gashes make the shell appear as 

 though cut into ribbons. The rotary mo\'ement gradually 

 subsides until a complete turning consumes twenty minutes, and 

 almost imperceptibly there follows a lull. An inactive almost 

 comatose condition pre\-ails for a period of about seventeen 

 hours. After the resting period, it appears that the egg pick is 

 no longer functional ; no new gashes are made, the embryo seeming 

 contented to concentrate its energies against the middle gash. 



