1896.] 



MICROSCOPICAL JOURNAL. 



293 



ubrium at the place of ectodermal thickening and form a 

 bud (fig. 5) while at the same time the ectodermal thicken- 

 ning is still furtlier increased by the formation of new cells 

 (a) — these cells being formed from the ectoderm alone. 

 The budcontinues its growth till ithecomes decidedly pear 

 shaped (fig. 6) and the mass of ectodermal cells has become 

 arranged in two layers (a) which have almost entirely 

 separated from the ectoderm. The endoderm has also 



grown out into the bud, forming a sort of cup. At the 

 next step (fig. 7), we find several marked changes. The 

 shape of the bud has changed from its pear-shape to 

 nearly spherical. The two cell layers of ectodermal ori- 

 gin have become separated,' forming a cavity (a) which 

 subsequently becomes what corresponds to the bell-shaped 

 cavity in the bell-shaped medusae of the Tubularian 



