96 M. O. Strobelt on the Anatomy and 



the same ovary, and is connected with the dorsal vessel as 

 already described. The ovarian tubes are enveloped by a 

 clear, structureless, tolerably strong membrane. Landois was 

 the first to make an accurate investigation of the course of 

 development in the chambers in Pediculus vestimentt, tracing 

 it step by step in the seven chambers. In that species this 

 was attended with less difficulty, because the most different 

 stages of development occur at the same time in the same 

 ovarian tube ; in the present case, on the contrary, I had to 

 examine a whole series of ovaries in order to obtain a clear 

 idea of the gradual progress of the development. I have, 

 however, arrived at exactly the same results as Landois, and 

 may therefore refer to them. I will here cite only one of his 

 principal statements (24, p. 50) : — u The cell situated in the 

 centre," he says, u is the germinal vesicle (fig. 11, kb), and 

 its nucleus the germinal spot ; the surrounding granular fluid, 

 containing small fat-molecules in suspension, is the vitellus 

 (fig. 11, d ) ; the rounded cells, already containing large 

 nuclear structures, placed in the upper part of the chamber 

 are the vitelligenous cells (fig. 11, ab), and the bacilliform i 



cells lying below them the epithelial layer of the germinal 

 chamber (fig. 11, estr)" In the further progress of the de- 

 velopment more and more of the vitelline mass is secreted, 

 the vitelligenous cells become smaller, the epithelium becomes 

 more coarsely cellular, and u at the approach of the maturity 

 of the ovum acquires the character of a rounded unistratified 

 layer, whereas it was previously cylindriform." The whole 

 vitellus becomes surrounded by an extremely fine and delicate 

 envelope, the so-called vitelline membrane. Last of all is 

 formed the external envelope of the ovum, the chorion, and, 

 indeed, from the epithelial cells by deposition externally. 

 The chorion is of considerable thickness and of firm con- 

 sistence. It is not textureless, like the vitelline membrane, 

 but exhibits on its surface numerous hexagonal areas, sepa- 

 rated from each other by grooves. Beneath these there is an 

 inner homogeneous layer of the chorion, which exceeds the 

 outer one in thicJcness. At the upper pole of the ovum, i. e. 

 at the end which is furthest from the uterus, when the ovum 

 has attained a certain stage of development, the operculum is 

 formed. Upon its production Leuckart (18) says, " Accord' 

 ing to my observations the operculum is produced in this way. 

 At a certain distance from the anterior pole of the ovum an 

 annular groove makes its appearance, which gradually pene- 

 trates deeper and deeper, and finally cuts through almost com- 

 pletely to the vitelline membrane." The complete separation 

 of the operculum, marked off by the groove in question, from j 





