OF THE LARVAL POLTPTEEUS. 333 



Section I. (PI. XXXV. %. 1) is taken through the twenty-fourth segment, and 

 shows the thickened strip of peritoneum in section lying to the outer side of the 

 mesentery of the genital ridge (ovary) and the more complicated arrangement of 

 tubules. 



Section II. (PL XXXV. fig. 2) is taken through the twenty-ninth segment, and 

 shows the thickened ridge (ov.d.) in section lying to the outer side of a small 

 projection which here represents the genital ridge (g.r.). It also shows the accessory 

 tubules on either side and the accessory glomerulus of the right side [k.t.a., ni.ci)s.a.). 

 The arrangement of the older tubules is here less complicated. 



Section III. (PL XXXV. fig. o) is through the thirtieth segment, and shows on the 

 left side a nephrostome opening upon the thickened ridge and communicating with 

 the glomerulus {^lejjh., m.cj)s.). On the right side accessory tubules are shown (k.t.a.). 



Section IV. (PL XXXV. fig. 4) is through the thirty-fourth segment ; on the left 

 side the edge of a nephrostome and also of a glomerulus is cut through [neph., m.cps.), 

 while on the right side is shown a single large glomerulus from Avhich a kidney-tubule 

 leads (m.cjys.). 



Section V. (PL XXXV. fig. 5) passes through the thirty-seventh segment, and shows 

 the openings of two kidney-tubules into the right and left segmental duct {k.t.). The 

 thickened ridge still persists, tliough the genital ridge does not extend so far back. 



Section VI. (PL XXXV. fig. 6) is very near the hind end of the body-cavity 

 behind the last kidney-tubules. The thickened ridge of peritoneum is still seen lying 

 under the segmental duct (ov.d., s.d.). 



Section VII. (PL XXXV. fig. 7) is right at the end of the body-cavity; the 

 segmental ducts are now turning ventralwards and approaching each other (s.d.), while 

 the thickened ridge still lies just ventral to them (ov.d.) 



Section VIII. (PL XXXV. fig. 8) passes just in front of the vent, behind the point 

 of union of the segmental ducts. The body-cavity is seen here to be prolonged 

 backwards in two portions on either side divided by a septum (b.c); in the upper 

 portions is still seen the thickened ridge of peritoneum (ov.d.). This upper portion is 

 the commencement of the folding-off of the oviduct from the body-cavity by the 

 forward growth of the septum, and it is at the point w that the oviducts eventually 

 open into the urinogenital sinus. The lower portion of the body-cavity ends 

 posteriorly at the point where the abdominal pores later break through (a.p.). 



The further stages in the folding-off of the oviducts from the body-cavity I have been 

 linable to observe, as in my next stage (9 cm.) the formation of the oviducts is already 

 complete, though their posterior ends still end blindly in the wall of the urinary 

 sinus. It is hardly possible to doubt, however, that the thickened ridge which we have 

 traced through the posterior portion of the body-cavity forms eventually the dorsal 

 wall of the oviduct. That is to say, we have, in the Polypterus larva, a row of nephro- 

 stomes opening into that portion of the body-cavity which will eventually become the 

 genital duct. 



3b2 



