318 IXSECTA. 



During the degeneration which takes place through the lateral 

 circumcrescence of the yolk by the germ-band (Figs. 171, 172), 

 the paired rudiment of the heart shifts more and more towards the 

 dorsal median line, and the genital rudiment connected with it by 

 means of the terminal filament follows it. This rudiment thus 

 comes to lie on the dorsal side of the developing enteron (Fig. 

 172, gz). 



The terminal filament (ef) originally represents a simple longi- 

 tudinally-placed epithelial plate. A rearrangement of its cells soon, 

 however, takes place, these becoming arranged in vertical rows, each 

 of which corresponds to a developing ovarian tube. In this way 

 the original plate-like terminal filament is broken up into the separate 

 terminal threads of the ovarian tubes (Fig. 173, ef). In this process, 

 however, the uppermost dorsal margin of the plate-like terminal 

 filament does not participate, but persists as an undivided filament 

 in the adult, where it is prolonged anteriorly and connects the 

 different ovarian tubes; this is the so-called Mailer's thread. The 

 latter is originally connected with the pericardial septum, but at a 

 later stage it appears to lose this connection. 



As the separate ovarian tubes, which in Phyllodromia number 

 about twenty, develop, they bend continuously inward from the 

 dorsal towards the ventral side of the ovarian rudiment (Fig. 173). 

 At the same time the epithelial cells (ep), some of which originally 

 lay between the genital cells, become arranged so as to form an 

 epithelium covering the surface of the ovarian tubes, this epithelium 

 further secretes on its outer surface a structureless cuticular tunica 

 propria. The outer peritoneal envelope of the ovaries is formed 

 from the cells of the surrounding fat-body. 



The genital rudiment originally, as we have mentioned, extended 

 from the second into the seventh abdominal segment. In the latter, 

 however, the genital cells are from the first few in number and 

 completely disappear later, so that the genital strand here seems 

 composed solely of epithelial cells. This part is the rudiment of the 

 oviduct proper, and forms a direct continuation of the cell-strand 

 (cz) mentioned above as lying ventrally to the genital cells, out of 

 which, as we have seen, the proximal, cup-shaped portion of the 

 oviduct is formed. The posterior section of the oviduct bends round 

 towards the ventral side, and becomes connected with the hypodermis 

 at the boundary between the seventh and eighth abdominal segments. 

 The rudiment of the oviduct is originally a solid strand, in which a 

 lumen forms later through the shifting apart of the cells. 



