68 On the Reproduction and Enibryogeny of the Aphides. 



above which they rise more or less. The whole mass of these 

 organs, the green colour of which being often very intense im- 

 mediately catches the eye, is composed of large oval or poly- 

 hedric cells, the characters of which I shall describe further on, 

 in speaking of the formation of the seminal corpuscles. A very 

 delicate envelope extends itself round each of them, and is con- 

 tinued to the posterior part in an attenuated process, which 

 loses itself upon the sides of the rectum, and probably represents 

 an excretory duct. As the neck of the seminal vesicle may 

 likewise be followed into this region, it is probably there that 

 the union of these ducts with the spermatic reservoir is effected. 

 As to the seminal vesicle, it is formed by a sac of considerable 

 size situated on the median line above the intestine, with its 

 fundus sometimes advancing nearly to the middle of the body. 

 Its wall is formed by a simple structureless membrane, a true 

 cell-membrane, of such delicacy and transparency that in most 

 cases its presence is betrayed only by the seminal corpuscles and 

 coloured granulations composing its contents — which explains 

 how it has remained undetected by all observers. The seminal 

 vesicle terminates by a very slender duct, which represents its 

 neck, and which I have been able to trace to the point of union 

 of the two ovarian tubes, where it is probably inserted. 



It remains for me, in conclusion, to say a few words about 

 the spermatic corpuscles and their formation. This commences 

 very early ; for ail the embryos of the viviparous Aphides at the 

 moment of their birth contain new generations in course of 

 development. Still more, it is not rare to find the spermatic 

 reservoir, to the early formation of which I have adverted above, 

 already filled with seminal corpuscles before there is any trace of 

 an embryo in the ovum. These corpuscles are formed, as I have 

 a;lready stated, in the large coloured cells which constitute the 

 mass of the two organs situated in the vicinity of the ovaries. 

 At the moment of their appearance these cells contained only a 

 homogeneous and colourless substance ; but as they enlarge they 

 become penetrated by fine granules, which give them the green 

 or yellowish-green colour presented by them in most Aphides ; 

 at the same time their contents become converted into a multi- 

 tude of little daughter cells, furnished with a membrane and a 

 nucleus : these are the cells of development of the spermatic 

 elements. They are, in fact, soon replaced by innumerable 

 small dark corpuscles of 0001-0002 millim. in diameter, which, 

 tinder a strong power, appear like minute Amoeba; but their 

 form does not change under the microscope. The large mother 

 Cells have then lost their transparency and their green colour, 

 and become opaque and brownish ; they are easily disintegrated, 

 breaking up into a sort of powder after the destruction of their 



