OVIPAROUS FEMALE. 119 



logically considered as a yolk-passage. If the yolk- 

 forming elements be immediately upon the yolk, with 

 broad surfaces, and without the separating epithelial 

 layers, then a perfect yolk-passage would seem to be 

 unnecessary, and its production (Zustandekommen) 

 difficult to realise.* 



The vagina of the viviparous female is furnished 

 with two muciparous or colleterial glands, the office of 

 which has been before indicated. The spermatheca 

 or sexual pouch is wanting in the organs of the agamic 

 female. 



3. REPRODUCTIVE ORGANS OF THE OVIPAROUS FEMALE 



APHIS. 



The reproductive organs of the oviparous female 

 have anatomically much in common with those of the 

 viviparous ; but the vulva sometimes terminates in a 

 short ovipositor, as may be seen in Drepanosiphum 

 and Phylloxera. This prolongation of the vulva is 

 figured in Pis. CXXI, fig. 1, CXXV, fig. 1. 



In Thelaxes dryojohila the vulva, which is always 

 situated between the eighth and ninth abdominal rings, 

 closes by a sphincter ; the action of this is controlled 

 by several bundles of contractile muscles, vide PI. E, 

 fig. 1. The opening thus may appear as a long slit 

 forming the lips of an oval. 



The vulva opens into a wide and thick-walled vagina, 

 which is provided with a longitudinal and transversely 

 striated muscular coat. After its continuation forward 

 for a short distance, it is perforated by the duct leading 

 from the colleterial glands, and shortly above this by 

 the opening from the spermatheca. 



Beyond this the vagina divides into two wide 

 branches, constituting the oviducts, which spread 

 towards each side of the body. Each of them finally 

 divaricates into five or more tubes, which end in the 

 ovarian chambers or ovisacs. 



* Idem, pp. 48, 51, Taf. iv, figs. 103—109, 130. 



