THE SEGMENTAL TUBES. 49! 



dilated portion of the segmental duct. The next important 

 change which they undergo consists in a junction being effected 

 between their posterior limbs and the segmental duct. In the 

 anterior part of the body these junctions appear before the 

 commencement of stage L. A segmental tube at this stage is 

 shewn in longitudinal section on PL 21, fig. jo,, and in transverse 

 section on PL 18, fig. 2. In the former the actual openings 

 into the body-cavity are not visible. In the transverse section 

 only one limb of the A is met with on either side of the section ; 

 the limb opening into the body-cavity is seen on the left side, 

 and that opening into the segmental duct on the right side. 

 This becomes quite intelligible from a comparison with the 

 longitudinal section, which demonstrates that it is clearly not 

 possible to see more than a single limb of the A in any transverse 

 section. 



After the formation of their junctions with the segmental 

 duct, other changes soon take place in the segmental tubes. By 

 the close of stage L four distinct divisions may be noticed in 

 each tube. Firstly, there is the opening into the body-cavity, 

 with a somewhat narrow stalk, to which the name segmental 

 tube will be strictly confined in the future, while the whole pro- 

 ducts of the original segmental tube will be spoken of as a seg- 

 ment of the kidney. This narrow stalk opens into a vesicle 

 (PL 1 8, fig. 2, and 21, fig. 6), which forms the second division. 

 From the vesicle proceeds a narrower section forming the third 

 division, which during stage L remains very short, though in 

 later stages it grows with great rapidity. It leads into the 

 fourth division, which constitutes the posterior limb of the A, 

 and has the form of a dilated tube with a narrow opening into 

 the segmental duct. 



The subsequent changes of each segment do not for the 

 most part call for much attention. They consist mainly in the 

 elongation of the third division, and its conversion into a coiled 

 tubulus, which then constitutes the main mass of each segment of 

 the kidney. There are, however, two points of some interest, 

 viz. (i) the formation of the Malpighian bodies, and (2) the 

 establishment of the connection between each segmental tube 

 and the tubulus of the preceding segment which was alluded 

 to in the description on p. 486. The development of the 



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