THE DEVEf.OPMENT OF PALUDINA VTVIPAT^A. 103 



the apex downwards, till its lumen is finally pnt into commu- 

 nication with that of the kidney, the opening being very 

 close to the reno-pericardial aperture. A reconstruction of 

 these organs from a series of transverse sections through an 

 embryo, with a well-coiled visceral hump, is shown in fig. 6, 

 The gonad [g.) is a hollow tube widening considerably at the 

 apex, in reality following the coils of the visceral hump, but 

 shown here spread out. The left kidney [1. h.) forms, as it 

 were, merely the proximal extremity of the gonad [g.), from 

 which it is separated at this time by no sharply marked histo- 

 logical differentiation. In this particular specimen the reno- 

 pericardial aperture {r.jjc.nj).) is retained even at this late 

 stage, and I have occasionally found it in other embryos of 

 about the same age ; more often it appears to be closed, but 

 it is difficult to tell for certain which is the normal condition, 

 as the opening is small and might become artificially closed 

 during preservation. In this case, however, the close proxi- 

 mity of the reno-pericardial and the reno-gonadial apertures 

 is well seen. Even at this late stage there is as yet no com- 

 munication between the loft kidney and its duct, but the 

 walls are now even more closely fused than before, and it is 

 obvious where the exact point of communication will be. 

 Details are shown in figs. 7, 8, and 9, which represent three 

 sections through the same embryo from which the reconstruc- 

 tion was made. Fig. 7, taken across the line a a in fig. G, 

 shows the left kidney (/. k.) with its opening into the pericar- 

 dium [r.j^c.ap.], and its blind end lying against the duct 

 {l.m.c), and nearly opening into it. Fig. 8 is the next 

 section, taken across the line h h, and again shows the new 

 pericardial aperture. Finally, fig. 9 is a section across the 

 widened extremity of the gonad at c c, showing the position 

 in the narrow space between the liver and the outer 

 epithelium of the body. 



All the essential relations between the different parts of 

 the genital apparatus are now established as in the adult, 

 and I have not followed their development in later stages. 

 It is interesting, however, in confirmation of the correctness 



