44^ 



Anfange des zweiten Monats aus einer einfachen Lage sehr zierlicher, 

 zart konturierter, polygonaler Zellen von 27—45 f.t Durchmesser mit 

 runden Kernen von 9 — 13 /.i und Kernkörperchen. Unter derselben 

 zeigen sich in einfacher zusammenhängender Schicht kleinere Zellen 

 von 6,8—9,0 jtt mit runden Kernen von 3,4—4,5 /i als erste Andeutung 

 der Schleimschicht." Farther on he states that this outer layer in 

 embryos of 6—7 weeks, seems to be in process of degeneration, while 

 below there appears a new and similar layer with smaller nuclei. 

 From my own observations I consider that the outer layer of poly- 

 gonal cells seen in the two-cells period, remains, and is transformed 

 into the layer of polygonal and domed cells seen in fig. 1. 



In embryos between 3 and 4 months old, we often find the outer 

 layer composed of 2 or 3 rows of cells. This is especially true of 

 the palms and soles, as shown Mn fig. 2, which represents the skin 



rM~ 







^i^!;^^.':.tl:.2^.1-^'^''^'4^N^ 



Fig. 2. Skin from palm, embryo of Sr^ month, e outer layer of bladder or epitrichial 

 cells. r.M rete Malpighii. 



from the palm in an embryo of between 3 and 4 months. There are 

 two rows of outer, granular cells which are very sensitive to the action 

 of coloring agents. These cells are irregular and polygonal shaped, 

 and in many cases there is still to be seen a large, deeply -stained 

 nucleus. The outer of these cells have a puffed out, bladder like 

 appearance, and the periphery is glistening and sharply defined. In 

 many instances the center of the cell seems to be empty, nothing re- 

 maining but the thickened, glistening walls. These cells I shall call 

 bladder cells, as they have been referred to by Zander as Blasen- 

 zellen. It is apparent that they are produced by a metamorphosis 

 of the outer polygonal cells, as a direct transition may be traced from 

 the polygonal slightly rounded forms of the 8 weeks old foetus, to the 

 domed and bladder-like cells best seen in the 3'^ month. These bladder 



