TESTES. 125 



in any common envelope. The corresponding organs 

 of Aphis jpadi, however, according to the researches of 

 Leuckarb, would seem to vary somewhat from this 

 general type ; and Prof. Balfour points out, also, that 

 there is something abnormal in the female organs of 

 this species. 



Balbiani states that the form and position of these 

 sperm-capsules vary at different ages of the insect. 

 In the larvae and pupse they appear as elongated sacs ; 

 in the adult they appear shorter and more ovoid. 



Each capsule is terminated by a short peduncle 

 which, communicating with its corresponding deferent 

 duct, finally unites into a single branch towards the 

 medial line of the body. Just below this point of 

 coalescence there are expansions of the walls of the 

 ducts, which Balbiani thinks are comparable to the 

 vesiculae seminales of other insects. These vesicles 

 descend in the form of two cords and insert themselves 

 close together into the ejaculatory tube. 



The sperm-capsules have a knotty or tuberculose 

 exterior, and when partly transparent they are highly 

 refractive to light.* 



The vasa deferentia are lined with epithelial cells, 

 which, however, can only be seen under treatment with 

 acetic acid, and under high magnifying powers. Male 

 Aphides have a single pair of muciparous glands, 

 the secretion from which probably forms a vehicle for 

 the transport of the spermatozoa through the efferent 

 passages. These muciparous glands of Aphis were 

 noticed by Morrens ; but he, like Leon Dufour, mistook 

 their nature, and considered them to be vesiculas 

 seminales. 



The ejaculatory canal ends at its posterior part 

 in a cul-de-sac or bulb, into which the deferent 

 vessels debouch ; and the other extremity terminates 

 at an orifice in the neighbourhood of two horny valves, 

 forming the copulative armature before alluded to. 



Balbiani has fully described the curious and highly- 



* Balbiani, ' Mem. s. 1. Gener, des Aphides,' 1. c, p. 55. 



