64 ON A PLATYPUS EMBRYO, \ 



often it is broken in the process of section cutting — a feature 

 Martin* has also met with in the case of the rabbit (c/. his fig. 7 

 A-D. Taf. vii. in this respect with our figs. 25 and 26). 



The Wolffian duct Anlage is now distinct not only from the 

 somites and lateral mesoderm, but also from the Anlage of the 

 tubules. However, it does again become connected with the 

 tubule Anlage, and also with the lateral mesoderm at its outer 

 edge, over a very short distance. The Anlage of the tubules 

 consists of a somewhat rounded mass in transverse section, with 

 its cells arranged in a radial manner round its somewhat clearer 

 centre. In this in some sections a distinct lumen occurs (fig. 26, 

 10. t.) The tubule Anlage is now only distinctly connected with the 

 lateral mesoderm, the connection with the somites being lost more 

 or less completely. Some sections indeed (fig. 26) show the 

 tubule Anlage as an isolated rounded mass, below which passes 

 a thin layer of loose cells of the intermediate cell mass. 



The duct varies somewhat in width in different sections, and 

 this gives rise to the irregular linear thickening previously 

 mentioned as seen in surface view. As it is traced to its distal 

 end the duct is found to be become gradually reduced to a thin 

 flat plate somewhat thicker in the middle and thinning off 

 laterally, and separated by a very small interval from the over- 

 lying thin area of the ectoderm. At the same time the Anlage of 

 the tubule becomes reduced in size and its differentiation from the 

 rest of the intermediate cell mass largely disappears, though it is 

 still distinguishable as a compact mass of rounded cells forming a 

 projection from the loose cells of the mass. 



In its posterior region the outer edges of the now very thin 

 Wolffian duct curve slightly upwards towards the ectoderm, and 

 thus the entire Anlage has here a somewhat arc-shaped appearance. 

 The duct is here of considerable width, though not more than two 

 cells in thickness in its middle region. Finally, with the upturned 

 edges of the Anlage, the ectoderm becomes continuous by means 

 of fine but very distinct strands (fig. 27, w.d.), and there is thus 



* Archiv f. Anat. 1888. 



