462 E. A. MINCHIN ON SOME DETAILS JN THE ANATOMY OF 



Entomologists are generally agreed in regarding the fleas as 

 modified and specialised Diptera that is to say, as descended 

 from fly-ancestors. If so, they may have once possessed a crop 

 such as is found in the fly, but which, with reduction in the size 

 of the body, has gradually disappeared, and has ceased to be 

 developed. Since, as has been pointed out, the crop is formed as 

 a diverticulum of the oesophagus, the existence of such an organ 

 in the ancestors of fleas might explain the persistence of a 

 musculature of this peculiar type in the oesophagus of the flea. 

 But it would be necessary to examine the oesophageal muscula- 

 ture of other insects before adopting this theory as an explana- 

 tion of the presence of stellate muscle-cells in the flea. 



DESCRIPTION OF PLATES. 



Plate 26. 



Abdominal Nervous Systems of the Male (left) and 

 Female (right) Flea, magnified 90 Diameters. 



th. 3 , metathoracic ganglion ; abd. 1 , abd. 3 , abd. 5 , and abd. 6 , first, 

 third, fifth, and sixth abdominal ganglia ; abd. 7 , 7th abdominal 

 ganglion, present in the male, wanting in the female ; T.g., 

 terminal ganglion-complex. Note the difference in the size and 

 number of the nerves that arise from T.g. in each case. 



Plate 27. 

 Salivary Glands of the Larval and Adult Flea. 



A, salivary gland of the larva, magnified 60 linear ; d., duct, 

 showing at its distal extremity (to the right) the union with the 

 corresponding duct from the other side of the body ; a small 

 portion of the duct is seen magnified 400 linear; r., reservoir; 

 l.a. 1 and l.a. 2 , the two anterior lobes of the gland ; l.p., the 

 posterior lobe. 



B and C, the salivary glands of the adult flea, at B magnified 

 60 diameters, for comparison with A, at C magnified 160; d., 

 duct ; gl., the two pouch-like glands. 



