358 GEORGE A. BATES 



shortened. The nuclei are so placed that their long diameter is 

 at right angles to the surface. The duct seems to lie in a groove 

 in the ectoderm which has been hollowed out for its reception. 

 The two sections are not consecutive, but are given to illustrate 

 the change iij the character of the ectoderm and the close relation 

 existing between it and the duct. Figure 40 is a section at the 

 extreme end of the anlage and has cut through the growing tip at 

 a point beyond the terminal cell into the clear cytoplasm which 

 the cell throws out in its advance along the ectoderm. This pe- 

 culiar feature of the growth of the anlage will be more clearly 

 demonstrated in the frontal sections to be described later. It 

 will be observed that the ectoderm seems to be grooved for the 

 reception of the duct, and also that there is a well defined hmiting 

 membrane between the two layers. These conditions are very 

 clearly shown in figure 41 which cuts through the anlage more 

 anteriorly and demonstrates more definitely the groove in the 

 ectoderm, as also the arrangement of the ectodermic cells for its 

 formation. 



In figures 42 to 47, drawn from sections of an embryo of 11 mm., 

 the duct is much larger than in the preceding series and comes into 

 contact with the ectoderm only at the extreme tip. The ectoderm 

 shows less modification and its cells have become much shorter 

 and more thickened. In some places the connection between the 

 anlage and the ectoderm is very close, as at figures 42 and 43. 

 This is at the extremity of the growing tip, but elsewhere the two 

 layers are widely separated and the connection between them has 

 been completely severed. The ectoderm shows the usual evi- 

 dences of modification, although the irregularity of its contour is 

 much less great and seems to be in less degree dependent upon 

 the presence of and contact with the anlage. 



Thus far the study has been confined largely to cross sections 

 and the evidence presented of the origin of the duct from the 

 pronephros and hence from the mesodermic somites, seems con- 

 vincing. This receives confirmation by the study of frontal sec- 

 tions where comprehensive views may be had of the two struc- 

 tures, ectoderm and duct, and their relation more extensively 



