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KINGSLEY. [Vol. VIII. 



(except that of change in the character of the cells) and this 

 in turn into the two limbs of the duct. In this series of sec- 

 tions a peculiarity is seen, which in most cases does not make 

 an appearance until a much later stage, viz. the formation of 

 trabeculse of mesodermal tissue which invade the cavity, and 

 passing from wall to wall of the proximal portion of the organ 

 tend to subdivide it and give it an anastomosing character. 



The changes which have occurred up to the Stage I are 

 represented in the horizontal sections (Figs. 6i a-c) and the 

 sagittal section (Fig. 62). Figs. 61 / and g are reconstruc- 

 tions by projection of the whole series of which a few sections 

 are represented in 61 a-e. The tube has now become more 

 elongate, extending in front nearly to the anterior limits of 

 somite IV, while the two limbs are relatively much more 

 closely applied to each other than before. With this growth 

 the regions are much more differentiated. The end sac (Fig. 

 6\ d) is separated from the, now numerous, lacunae of the 

 mesoderm by a layer of pavement epithelium which in my 

 series nowhere shows a break.^ This coelomic sac passes 

 directly, as before, into the nephrostome {nst) and this again 

 into the duct, which shows no change, except increase in 

 length, until in the distal limb, when about at the level of the 

 end sac it becomes enlarged into an excretory vesicle or 

 bladder, ev. (Figs. 60 and 61 f, g). 



Later than Stage I, I have comparatively few notes which 

 add to the information contained in my earlier paper ('85) and in 

 the simultaneous one by Mr. Gulland ('85). One reconstruction, 

 however, demands attention ; that represented in Fig. 62. 

 This is the nephridium in Stage K just before the molt in 

 which the telson appears in the adult form. One error how- 

 ever is noticeable in it ; the lateral amplification is too great 

 and consequently the diameter of the tubes and the extent of 

 the outgrowths are exaggerated. In this the same parts are 

 recognizable as before but they have undergone some modifica- 

 tions. Thus in the region of the end sac a fenestration is 



1 In my earlier paper I was in doubt upon this point and thought that possibly 

 {'85, p. 535) I had found such an opening, which led to the reconstruction of the 

 tube with an internal funnel. Still I was not positive. I now feel confident that 

 the opening of that paper was an artifact. 



