128 



figures show conclusively that naturally infected rats are not infected 

 by feeding. It is curious, as has been pointed out by McCoy (4), that 

 such a large percentage of cervical buboes should be found in India, 

 while a cervical bubo has been seen but once in naturally infected 

 animals in San Francisco. Here the axillary and inguinal buboes are 

 the rule. The Indian Commission found that the commonest situa-. 

 tion to find fleas on guinea pigs was the head and neck. They 

 combed 53 guinea pigs to determine the regional distribution of fleas, 

 and found that 65.3 per cent were taken from the neck and head. 

 This would account for the preponderance of cervical buboes in 

 guinea pigs observed in their work, and inferentially for the pre- 

 ponderance of cervical buboes found in naturally infected rats. 

 Thinking that the predominating rat flea in San Francisco, the 

 CeratophyUus fasciatus, might be the carrier of the infection and that 

 it might prefer a different part of the body than the LoemopsyUa 

 cheopis, McCoy and Mitzmain carried on a series of investigations to 

 determine the regional distribution of fleas on the rat's body, but 

 this has shown that while the CtenopsyUus musculi seems to be gen- 

 erally confined to the head and neck, the CeratophyUus fasdatus and 

 Lcemopsylla cheopis are almost invariably taken from the body, 

 especially from the pelvic region. 



ANATOMY OF THE MOUTH PARTS OF THE CERATOPHYLLUS FASCIATUS. 



The following description differs somewhat from that given by 

 Wagner (5) and the description found in the Journal of Hygiene, both 

 of which, however, refer to different species of Siphonaptera. 



The mouth parts may be divided into those inside and those outside 

 of the head. 



OUTSIDE THE HEAD. 



The epipharynx, or pricker, is a long, slender, hollow organ. Its 

 cavity is closed distally, and proximally connects with the hoemocoel. 

 It is made up of a dorsal and a ventral portion. Its dorsal portion 

 ends just within the head. Its ventral portion is grooved and is 

 continuous with the posterior wall of the aspiratory pharynx. Its 

 distal extremity is slightly expanded, forming a stylet for piercing, 

 while the little papillae seen along the anterior surface in many species 

 are absent in this one. Laterally there is a membranous expansion 

 which interlocks with a similar expansion on the mandibles, forming 

 a tube, through which the blood is sucked. 



The mandibles are two in number, articulating just within the 

 head, so that they are capable of independent movement. They are 

 serrated at their distal extremities. Above, within the head, the 

 anterior portion of the mandibles ends just behind the beginning of 

 the h3rpopharynx, to which it is connected, becoming practically con- 

 tinuous with that organ. The posterior portion is attached to its 



