of a Species of Chironomus. 39 



In our larva tliej are concealed among the adipose bodies 

 {corpora adiposa)^ being situated in the seventh abdominal 

 segment on each side of the intestine (fig. 3,o), so that they can 

 only be seen occasionally during the movements of the adipose 

 bodies and intestine ; and if we wish to study them more 

 continuously, we are compelled to have recourse to compres- 

 sion with the glass cover, as has already been stated by 

 Leuckart*. Their intimate structure, however, can be studied 

 only by preparation, by cutting or pressing them out. 



To return to the developmental history of the ovary. The 

 bodies, or composite cells, which we have seen in the em- 

 bryonal ovary, representing the rudiments of the ovarian 

 tubes, consist of a homogeneous protoplasm, in which the 

 nuclei derived from the embryonal cells lie ; among these 

 nuclei the largest may easily be distinguished, as it only 

 contains one nucleolar corpuscle, whilst the others, formerly 

 embryonal cells, contain usually two, but sometimes even three. 

 The large nucleus represents the nucleus of the cell, and origi- 

 nated, as we have already seen, from the nucleus of the polar 

 cell ; the whole structure, however, is nothing but a composite 

 membraneless cell. Somewhat later we observe an elongation 

 of this cell,* and at the same time a membrane {tunica propria) 

 is developed, which apparently originates from the protoplasm. 

 Beneath this tunica propria there is a layer of fine epithelial 

 cells, produced by the continued division of the embryonal 

 cells. 



The residuary nuclei of the ovarian tubes remain in the 

 protoplasm, and now form the so-called formative cells of the 

 vitellus ; and the whole cell may now receive the name of an 

 ovarian tube. Metschnikow, indeed, states that the formative 

 cells of the vitellus originate from the nuclei of the polar cells, 

 and the epithelial cells from the embryonal cells f, so that the 

 ovum has nothing in common with the epithelial cells — "that 

 the germ-cells stand in no genetic relation to the epithelial 

 cells, and that only the germigenous and vitelligenous cells 

 are of common origin "f . But, in accordance with our direct 

 observations, we must differ from Metschnikow's opinion, in- 

 asmuch as we deduce the genesis of both the vitelligenous 

 and the epithelial cells from the embryonal cells. 



These ovarian tubes, as Ave already know, pass into thin 

 filaments, which are covered by a common membrane (the 

 peritoneal envelope of the entire ovary), represent the un- 

 developed parts of the ovarian tubes §, and probably serve 



* Loc. cit. p. 290, 



t Embryologisclie Studien, p. 32. J Ihid. p. 104, 



§ Der Eierstock und die Samentasche der Insecten, p. 49, 



