456 E. A. MINCHIN ON SOME DETAILS IN THE AK ATOMY OF 



combine clearly in one sketch things seen in the microscopic 

 preparation at different foci. 



Seen in life, that is to say in a freshly dissected flea, the cork- 

 screw-organ is usually performing peculiar pulsating movements, 

 which remind one to some extent of the movements of the hair- 

 spring of a watch, with the difference that the hairspring lies in. 

 one plane, while in the organ of the flea the axis of the spiral i& 

 prolonged vertically so that a form like a corkscrew results. It 

 is seen that in the living condition the corkscrew becomes alter- 

 nately first longer and narrower and then shorter and broader. 

 The elongation and narrowing of the corkscrew is doubtless 

 brought about by the contraction of the radiating superficial 

 muscles ; these in their turn are antagonised by the spiral muscle, 

 which by its contraction would tend naturally to make the cork- 

 screw shorter and broader. 



As to the function of corkscrew- organ, I can only offer the 

 suggestion that it may act as a sort of sperm -pump. The move- 

 ments seen in the freshly dissected flea may perhaps become more 

 active and regularly rhythmical during the act of copulation, 

 and serve to pump the sperm on from the ductus ejaculatorius 

 and vasa deferentia into the penis. This is, of course, a mere 

 conjecture from the observed facts of its structure and activity. 

 If, on the other hand, the cushion of cells between the spiral 

 muscle and the duct be glandular in nature, the organ as a 

 whole must have other functions in addition to that of acting 

 as a pump. 



The penis is an organ of complicated structure, which I will 

 deal with briefly ; PI. 29 shows what I have been able to make 

 out in preparations mounted unstained, or further cleared with 

 potash before mounting. The penis (P.), which is very large in 

 proportion to the size of the insect, is made up of strong thick 

 bars of chitin. It is worked mainly by strong protractor and 

 retractor muscles attached to a broad bar of chitin (b 1 ), which is 

 a prolongation of the dorsal integument at the right and left 

 margins of the pygidium. The median retractor muscles (m.r.) 

 are attached distally to a prolongation of the dorsal side of the 

 penis, and the lateral retractors (l.r.m.) are attached to a bar (b 2 ) 

 which arises from the ventral side of the penis; there are two such 

 bars, right and left, diverging from one another like aV; it is 

 clearly impossible that the penis could be protruded farther from 



