oil) DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. 



The cleft first visible on the dorsal half, and appearing semi- 

 lunar in tiansverse section, is completed by the anal cavity. 

 If a horizontal section be now carried through the inferior pole, 

 the fissure is seen to be circular. Close to the inferior pole the 

 circle becomes somewhat smaller, and ceases with the freely 

 exposed groove of Rusconi. A funnel-shaped space thus com- 

 mences at this groove, which is occupied by the plug composed 

 of white germ cells (yolk plug, Dotter-propf, Ecker). As the 

 canal in which the outermost portion of the cone sticks 

 gradually contracts, the white area becomes so small as to be 

 perceptible only as a white point. At a later period this also 

 disappears, and there remains only a canal still recognizable in 

 sections, and with high magnifying powers, which all authors 

 have designated the anal opening. And now, when the 

 extremely attenuated plug of white cells retracts or tears 

 away, (as at least in all probability occurs in Bufo cinereus,) 

 Rusconi's groove communicates with the anal cavity through- 

 out its whole extent. A small annular swelling, visible 

 even to the naked eye, on the outer wall of this cavity, still 

 indicates the point where the yolk plug formerly interrupted 

 ihe cavity, and the depression in the swelling is a guide to the 

 spot where the section should be carried if it be desired to 

 hit the canal at its embouchure. 



In the meanwhile the ovum has undergone its rotation ; the 

 meridian has become its sequator; the anal opening has a lateral 

 position, the dorsal half being superior, and the abdominal 

 half, with the annulus of germ cells projecting strongly 

 towards the food cavity, being inferior. In the latter, some 

 remains of the cleavage cavity of Baer are long preserved. 



The ovum may still be regarded as a vesicle enclosed by 

 laminated walls, except that in the lower half of the vesicle 

 the innermost lamina is pushed inwards by a mass or hillock 

 of gerrn cells. The various laminae, however, do not present 

 the same thickness throughout. I must here draw this account 

 to an abrupt conclusion, because these differences already con- 

 stitute the beginnings of the rudimentary organs, which cannot 

 in this work be further discussed. 



(&.) THE GERM OF THE FOWL. In the egg of the Fowl, the 



