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HARDWICKE'S SCIENCE-GOSSIP. 



shape, the most common shape being somewhat of an 

 oval. Usually in flies the first tarsal joint is well 

 supplied with muscles, nerves, tracheal vessels, and 

 an apodeme, this latter extending to the terminal 

 joint of the tarsus, but in the same joint, in Hilara 

 pilosa, muscles are absent, the space which they 

 should occupy being filled with large glands, from 



hairs with which its under surface is covered." 

 Having tried to confirm this statement, I have failed 

 to convince myself of its correctness, though the 

 attempt has resulted in bringing out other facts which 

 may be of some interest. The minuteness of the 

 parts prevents satisfactory results being obtained by 

 dissection, I have therefore made sections in various 



Fig. 47.— Hilara Jiilosa, longitudinal section through first joint of anterior tarsus of male ; a, outer wall ; I, inner wall ; 



gg, glands ; d, ducts. 



which well-defined iducts extend to the integument, 

 on the inner side of the foot (Fig. 47). Some of the 

 ducts in their course turn upon themselves, forming 

 loops before penetrating the integument, which they 

 do immediately above each large hair. The orifice 

 of the duct is circular, and placed so close to the 

 base of the hair that the minutest drop of fluid 

 exuded would necessarily come in contact with it. 

 I have not had an opportunity of examining the 

 secretion, but it is most probably of a viscid nature, 

 and like that given off from the pulvilli of flies. 

 Similar glands I have found in the anterior tarsi of 

 the water-beetle, Asilus sulcatum, which are in 

 intimate connection with both the large and small 

 so-called sucking discs. The use of this fluid has 

 not been absolutely determined, but it is thought to 

 be of service to the insect during the act of co- 

 pulation. 



The idea that the pulvilli or pads on the feet of 

 flies act as suckers to enable the insect to walk in an 

 inverted position on ceilings, etc., has not yet been 

 eradicated from the minds of some people, though a 

 sufficient proof has long been established showing 

 that an adhesive fluid, exuded by the pulvilli, enables 

 them to perform this feat. But where, and by what 

 means, is this fluid elaborated? In Mr. Lowne's 

 Monograph on the Blow-fly, it is stated that "a close 

 sac fills the whole of the last four tarsal joints, and 

 is lined with pavement epithelium ; it secretes a 

 perfectly clear, viscid fluid, which exudes from it 

 into the pad and fills its cavity, as well as the hollow 



directions through both the tarsal joints and pulvilli 

 of numerous flies, and have invariably found in the 

 posterior portion of the pulvilli a number of secreting 

 glands, but in no instance have I met with glands in 

 any of the four last tarsal joints. The number of 

 glands varies much in different species of flies, the 

 most numerous I have met with are in the pulvilli of 



Fig. 48.— Longitudino-vertical section of pulvillus of 

 Sarcophaga carnaria. 



Sarcophaga carnaria, a troublesome fly of medium 

 sire with abnormally large flat pulvilli. Fig. 48 

 represents a portion of a longitudino-vertical section 

 of S. carnaria. The upper wall (a) is arched, and 

 formed of semi or half-tubes of pigmented chitin laid 

 lengthwise close together, with the round side upper- 

 most. The lower wall (/>) is not parallel with the 

 upper, but forms continuous curves in both longi- 

 tudinal and transverse directions, causing the fine 

 transparent hairs with which it is closely beset, to 

 assume various angles. This irregular contour of the 



