12G BRITISH APHIDES. 



complicated penis, which is a true intromittent organ. 

 According to his explanation the erection is caused by 

 a regular turning inside out (renverser au dehors), 

 like the finger of a glove. It is caused by a pressure 

 from behind ; and it can be therefore easily made to 

 protrude by artificial squeezing. 



The penis may easily be seen to be composed of two 

 independent membranous tubes, one within the other. 

 The interior tube is much plicated, and is somewhat 

 of a resistant nature. It shows no direct attachment 

 except through the connections with the deflecting 

 ducts and the accessory glands, the secretions of 

 which pass directly into its cavity. The copulative 

 armature consists mainly of two chitinous valves ; 

 which by their approximation protect and perhaps 

 compress the genital opening. 



Two pilose mammiliform processes are connected 

 with the semicircular border-plate of the orifice, but 

 their exact import is obscure. Probably they act as 

 compressors.* 



From the inverting action of the penis it is obvious 

 that the four separate ducts which are attached to its 

 posterior portion are drawn into the inner channel at 

 the moment of its protrusion. 



The great size of this organ is remarkable. In 

 some cases it equals one third of the length of the 

 animal's body. A notable example of such may be 

 seen in Chcrmcs abietis which I have figured. The 

 sebific glands of the male may be considered, perhaps, 

 homologous to the collctcrial glands of the female. 



In most male Aphides from three to five sperm- 

 capsules may be counted as ranged in fascicles on 

 each side of the body. In the species Siphonophora 

 millefolii, Drepanosiphv/m platanoides, and Aphis pcr- 

 sicce, each lateral fasciculus contains six capsules; 

 but the number appears to be inconstant in species of 



* For plates illustrating the above see vol. iv, Plate CXVIII, fig. 8, 

 and Plate G. The principal figure relating to the male organ is copied 

 from Balbiani's Memoir above cited. Some of the smaller details are 

 also drawn from the same source. 



