G. CarJ lluber 15 



Schreiner, pages 1"21 to 128 and pages 138 to 14().) The further devel- 

 opment of the primary renal pelvis and nephrogenic tissue is for cat, 

 pig, and human embryos mucli the same as above described for the 

 rahbit. For each type, with the appearance of the primary renal branches 

 of the primary renal pelvis, the inner and outer zones of the nephrogenic 

 tissue may be clearly made out, the inner zone breaking up into cell 

 groups which enclose and surround the ends of the branches as these 

 become differentiated. x\t this stage, the primary renal pelvis for each 

 type studied and modeled presents a middle portion of somewhat irregu- 

 lar shape, the primary renal pelvis proper, from which arises the ureter 

 and an anterior and caudal end, slightly enlarged and more or less lobu- 

 lated (depending on the stage of development) and three pairs of branches 

 connected with the middle portion; these are not, however, made out 

 with the same degree of clearness and do not present quite the same 

 arrangement in the different types studied. These three pairs of branches 

 are quite readily made out in cat embryos and present an arrangement not 

 unlike that seen in the rabbit (text-figure 21 B, Schreiner), while in pig 

 embryos the grouping of the primary branches is not so regular and only 

 after they have attained some size is it possible to make out clearly what 

 may be regarded as three pairs of branches. This, thougli to a less extent, 

 is true also of human emljryos. Attention may, however, here be called to 

 the fact that models of the primary renal pelvis and its branches, in 

 embryos of the same genus and of about the same age, even of the two 

 kidneys of the same embryo (irrespective of size) present slight variation 

 in the form of the primary renal pelvis and in the arrangement of the 

 branches. A difference is also noted in the different types in the shape of 

 the ureter as it enters the primary renal pelvis. In rabbit and cat em- 

 bryos, this presents only a slight funnel-shaped expansion, while in pig 

 and human embryos the expansion is much greater and is compressed in a 

 dorso-ventral direction with its long axis parallel to that of the renal pel- 

 vis. The enlarged anterior and caudal ends of the primary renal pelvis, 

 soon after the anlage of the three pairs of branches to which reference 

 has been made, present, as development proceeds, more and more marked 

 irregularity of form and develop each two, sometimes three, branches, 

 which in appearance are like the other branches, showing a slightly nar- 

 rowed stalk and enlarged ends ; at the same time, the inner zone of the 

 nephrogenic tissue which enclosed and surrounded the enlarged ends of 

 the primary renal pelvis, breaks up into masses which surround only the 

 bulbous ends of the resulting branches. In Fig. I, .1 and B, are repro- 

 duced two models, obtained by wax reconstruction, of the ureter, renal 

 pelvis and branches of a cat and a human embryo for a stage slightly older 



