THE OVARIA OF INSECTS. 381 



capsular epithelium, but to large vltelligenous cells. These 

 stay in the dilated anterior chamber of the ovarian tube. 

 But each ovum is originally connected by continuity of sub- 

 stance with one of these cells, and the pedicle of connection 

 may be traced even to the second and third ovum. It seems 

 probable, therefore, that these " vitelhgenous cells," for some 

 time, supply material to the growing ova. 



In most insects, similar vitelhgenous cells are found ; but 

 they are situated at the anterior end of each ovicapsule, so 

 that, as the column of ovicapsules lengthens by the addition 

 of new ovicapsules to its anterior end, the vitelhgenous cells 

 are interposed between every two ova. The vitelline mem- 

 brane and the chorion first invest the posterior extremity and 

 the sides of the ovum ; and, for some time, leave an opening 

 at the end of the ovum adjacent to the vitelligenous cells. 

 This opening is usually only partially closed, and w'hat re- 

 mains of it constitutes the aperture or apertures, termed the 

 onicropyle^ through which the spermatozoa enter when the 

 egg is fecundated. The vitelligenous cells usually remain 

 outside the ovum, and eventually undergo degeneration ; but, 

 in many Diptera, they become inclosed within the coats of tlie 

 ovum and their substance is merged in that of the vitellus. 



Dr. A. Brandt has proposed the term py^'^noistic for ovaries 

 of the first mode, and meroistic for those of the second and 

 third modes of development of the ova here described. So 

 far as is at present known, only the Oithoptera and the Puli- 

 cidm possess panoistic ovaria. 



The peritoneal coat of the ovarioles is a cellular struct- 

 ure, containing many tracheae and, frequently, muscular fibres. 

 It is usually extended beyond the anterior end of each ovari- 

 ole into a filamentous process, which, after uniting with those 

 of the other ovarioles of the same side, is continued into the 

 pericardial tissue. At its opposite extremity it passes into 

 the walls of the oviduct, which are muscular and are lined by 

 an epithelium. 



The development of the ovaria has been traced in Dijjtcra 

 and Ziepidoptera. Each ovary is, at first, a rounded mass of 

 indifferent tissue, from which a filiform prolongation is given 

 off backward ; this has not been traced into connection with 

 any other organ, and appears to terminate by a free end. 

 The mode of origin of this rudimentary, or primary, ovarium 

 is unknown, but the first step toward the formation of the 

 genital organs is the separation of the peripheral indifferent 

 tissue from the central portion, and the division of the latter 



