692 
J. DAVIDSON. 
Other authors, and the “ Secuudiire Dotter ” described by 
^lecznikow (1866) in Coccidte. Witlaczil (1882) has 
described them iii Aphis, Krassilstschik (1892) in Phyl- 
loxera, Dreyfus (1894) in Phylloxera, Mordwilko (1895) 
in Traina, and Grove (1909) in Siphonophoraj so that 
they appear to be generally present throughout the Aphi- 
di das and probably the Cocci dm. 
The origin and development of the pseudovitellus cells 
have been described by Will (1888) and also by Witlaczil 
(1884), but the function of these cells does not appear to be 
established. The appearance and distribution of them in the 
individual depends upon the stage of its development. In 
embryos of S. lanigera they form a conspicuous lobed mass 
of cells in the posterior region of the body. In mature, 
apterous viviparous females however, they degenerate into 
groups of two, three or more cells, lying to the side of the 
ovarian cmca in the posterior region of the body. I have 
observed in a few individuals, isolated pseudovitellus cells in 
the thoracic region of the body. 
It would appear that these cells fulfil a nutritive function 
for the developing embryos, but Witlaczil (1882) considers 
them to be excretory in function. 
Mordwilko (1895, p. 357) has briefly descifibed the changes 
which take place in the pseudovitellus during the develop- 
ment of Tram a. According to this author, the cells in 
young embryos of Trama form a tubular layer lying above 
the rectum, which, as the embryo develops, divides into three 
finger-like, longitudinal lobes, lying between the ovarian 
ceeca. In mature adults only two cell masses are seen, which 
lie to the side of the body in the fifth and sixth segments, and 
these cells show signs of degeneration. 
In addition to the pseudovitellus cells described above, 
there are in S. lanigera a few large cells situated in the 
])Osterior region of the body, which have a dirty-greyish, 
coarsely granular cell contents and a small nucleus (fig. 45, 
y. c.). When stained with hmmatoxylin and eosin they differ 
in appearance from the pseudovitellus cells, the cytoplasm 
